crypto: hw_random - Add new Exynos RNG driver

Replace existing hw_ranndom/exynos-rng driver with a new, reworked one. This is a driver for pseudo random number generator block which on Exynos4 chipsets must be seeded with some value. On newer Exynos5420 chipsets it might seed itself from true random number generator block but this is not implemented yet.

New driver is a complete rework to use the crypto ALGAPI instead of hw_random API. Rationale for the change:
1. hw_random interface is for true RNG devices.
2. The old driver was seeding itself with jiffies which is not a reliable source for randomness.
3. Device generates five random numbers in each pass but old driver was returning only one thus its performance was reduced.

Compatibility with DeviceTree bindings is preserved.

New driver does not use runtime power management but manually enables and disables the clock when needed. This is preferred approach because using runtime PM just to toggle clock is huge overhead.

Another difference is reseeding itself with generated random data periodically and during resuming from system suspend (previously driver was re-seeding itself again with jiffies).

Signed-off-by Krzysztof Kozlowski <[email protected]>

---
 MAINTAINERS                         |   8 +
 drivers/char/hw_random/Kconfig      |  14 --
 drivers/char/hw_random/Makefile     |   1 -
 drivers/char/hw_random/exynos-rng.c | 231 ---------------------
 drivers/crypto/Kconfig              |  15 ++
 drivers/crypto/Makefile             |   1 +
 drivers/crypto/exynos-rng.c         | 390 ++++++++++++++++++++++++++++++++++++
 7 files changed, 414 insertions(+), 246 deletions(-)
 delete mode 100644 drivers/char/hw_random/exynos-rng.c
 create mode 100644 drivers/crypto/exynos-rng.c

MAINTAINERS +8 -0

index affecc6d59f4..371fda859d43 100644
@@ -10977,6 +10977,14 @@ L:     alsa-devel at alsa-project.org (moderated for non-subscribers)
 S:     Supported
 F:     sound/soc/samsung/
 
+SAMSUNG EXYNOS PSEUDO RANDOM NUMBER GENERATOR (RNG) DRIVER
+M:     Krzysztof Kozlowski <[email protected]>
+L:     linux-crypto at vger.kernel.org
+L:     linux-samsung-soc at vger.kernel.org
+S:     Maintained
+F:     drivers/crypto/exynos-rng.c
+F:     Documentation/devicetree/bindings/rng/samsung,exynos-rng4.txt
+
 SAMSUNG FRAMEBUFFER DRIVER
 M:     Jingoo Han <[email protected]>
 L:     linux-fbdev at vger.kernel.org

drivers/char/hw_random/Kconfig +0 -14

index 0cafe08919c9..bdae802e7154 100644
@@ -294,20 +294,6 @@ config HW_RANDOM_POWERNV
 
          If unsure, say Y.
 
-config HW_RANDOM_EXYNOS
-       tristate "EXYNOS HW random number generator support"
-       depends on ARCH_EXYNOS || COMPILE_TEST
-       depends on HAS_IOMEM
-       default HW_RANDOM
-       ---help---
-         This driver provides kernel-side support for the Random Number
-         Generator hardware found on EXYNOS SOCs.
-
-         To compile this driver as a module, choose M here: the
-         module will be called exynos-rng.
-
-         If unsure, say Y.
-
 config HW_RANDOM_TPM
        tristate "TPM HW Random Number Generator support"
        depends on TCG_TPM

drivers/char/hw_random/Makefile +0 -1

index 5f52b1e4e7be..6f1eecc2045c 100644
@@ -24,7 +24,6 @@ obj-$(CONFIG_HW_RANDOM_OCTEON) += octeon-rng.o
 obj-$(CONFIG_HW_RANDOM_NOMADIK) += nomadik-rng.o
 obj-$(CONFIG_HW_RANDOM_PSERIES) += pseries-rng.o
 obj-$(CONFIG_HW_RANDOM_POWERNV) += powernv-rng.o
-obj-$(CONFIG_HW_RANDOM_EXYNOS) += exynos-rng.o
 obj-$(CONFIG_HW_RANDOM_HISI)   += hisi-rng.o
 obj-$(CONFIG_HW_RANDOM_TPM) += tpm-rng.o
 obj-$(CONFIG_HW_RANDOM_BCM2835) += bcm2835-rng.o

drivers/char/hw_random/exynos-rng.c deleted +0 -231

deleted file mode 100644
index 23d358553b21..000000000000
@@ -1,231 +0,0 @@
-/*
- * exynos-rng.c - Random Number Generator driver for the exynos
- *
- * Copyright (C) 2012 Samsung Electronics
- * Jonghwa Lee <[email protected]>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation;
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
- *
- */
-
-#include <linux/hw_random.h>
-#include <linux/kernel.h>
-#include <linux/module.h>
-#include <linux/io.h>
-#include <linux/platform_device.h>
-#include <linux/clk.h>
-#include <linux/pm_runtime.h>
-#include <linux/err.h>
-
-#define EXYNOS_PRNG_STATUS_OFFSET      0x10
-#define EXYNOS_PRNG_SEED_OFFSET                0x140
-#define EXYNOS_PRNG_OUT1_OFFSET                0x160
-#define SEED_SETTING_DONE              BIT(1)
-#define PRNG_START                     0x18
-#define PRNG_DONE                      BIT(5)
-#define EXYNOS_AUTOSUSPEND_DELAY       100
-
-struct exynos_rng {
-       struct device *dev;
-       struct hwrng rng;
-       void __iomem *mem;
-       struct clk *clk;
-};
-
-static u32 exynos_rng_readl(struct exynos_rng *rng, u32 offset)
-{
-       return  readl_relaxed(rng->mem + offset);
-}
-
-static void exynos_rng_writel(struct exynos_rng *rng, u32 val, u32 offset)
-{
-       writel_relaxed(val, rng->mem + offset);
-}
-
-static int exynos_rng_configure(struct exynos_rng *exynos_rng)
-{
-       int i;
-       int ret = 0;
-
-       for (i = 0 ; i < 5 ; i++)
-               exynos_rng_writel(exynos_rng, jiffies,
-                               EXYNOS_PRNG_SEED_OFFSET + 4*i);
-
-       if (!(exynos_rng_readl(exynos_rng, EXYNOS_PRNG_STATUS_OFFSET)
-                                                & SEED_SETTING_DONE))
-               ret = -EIO;
-
-       return ret;
-}
-
-static int exynos_init(struct hwrng *rng)
-{
-       struct exynos_rng *exynos_rng = container_of(rng,
-                                               struct exynos_rng, rng);
-       int ret = 0;
-
-       pm_runtime_get_sync(exynos_rng->dev);
-       ret = exynos_rng_configure(exynos_rng);
-       pm_runtime_mark_last_busy(exynos_rng->dev);
-       pm_runtime_put_autosuspend(exynos_rng->dev);
-
-       return ret;
-}
-
-static int exynos_read(struct hwrng *rng, void *buf,
-                                       size_t max, bool wait)
-{
-       struct exynos_rng *exynos_rng = container_of(rng,
-                                               struct exynos_rng, rng);
-       u32 *data = buf;
-       int retry = 100;
-       int ret = 4;
-
-       pm_runtime_get_sync(exynos_rng->dev);
-
-       exynos_rng_writel(exynos_rng, PRNG_START, 0);
-
-       while (!(exynos_rng_readl(exynos_rng,
-                       EXYNOS_PRNG_STATUS_OFFSET) & PRNG_DONE) && --retry)
-               cpu_relax();
-       if (!retry) {
-               ret = -ETIMEDOUT;
-               goto out;
-       }
-
-       exynos_rng_writel(exynos_rng, PRNG_DONE, EXYNOS_PRNG_STATUS_OFFSET);
-
-       *data = exynos_rng_readl(exynos_rng, EXYNOS_PRNG_OUT1_OFFSET);
-
-out:
-       pm_runtime_mark_last_busy(exynos_rng->dev);
-       pm_runtime_put_sync_autosuspend(exynos_rng->dev);
-
-       return ret;
-}
-
-static int exynos_rng_probe(struct platform_device *pdev)
-{
-       struct exynos_rng *exynos_rng;
-       struct resource *res;
-       int ret;
-
-       exynos_rng = devm_kzalloc(&pdev->dev, sizeof(struct exynos_rng),
-                                       GFP_KERNEL);
-       if (!exynos_rng)
-               return -ENOMEM;
-
-       exynos_rng->dev = &pdev->dev;
-       exynos_rng->rng.name = "exynos";
-       exynos_rng->rng.init =  exynos_init;
-       exynos_rng->rng.read = exynos_read;
-       exynos_rng->clk = devm_clk_get(&pdev->dev, "secss");
-       if (IS_ERR(exynos_rng->clk)) {
-               dev_err(&pdev->dev, "Couldn't get clock.\n");
-               return -ENOENT;
-       }
-
-       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
-       exynos_rng->mem = devm_ioremap_resource(&pdev->dev, res);
-       if (IS_ERR(exynos_rng->mem))
-               return PTR_ERR(exynos_rng->mem);
-
-       platform_set_drvdata(pdev, exynos_rng);
-
-       pm_runtime_set_autosuspend_delay(&pdev->dev, EXYNOS_AUTOSUSPEND_DELAY);
-       pm_runtime_use_autosuspend(&pdev->dev);
-       pm_runtime_enable(&pdev->dev);
-
-       ret = devm_hwrng_register(&pdev->dev, &exynos_rng->rng);
-       if (ret) {
-               pm_runtime_dont_use_autosuspend(&pdev->dev);
-               pm_runtime_disable(&pdev->dev);
-       }
-
-       return ret;
-}
-
-static int exynos_rng_remove(struct platform_device *pdev)
-{
-       pm_runtime_dont_use_autosuspend(&pdev->dev);
-       pm_runtime_disable(&pdev->dev);
-
-       return 0;
-}
-
-static int __maybe_unused exynos_rng_runtime_suspend(struct device *dev)
-{
-       struct platform_device *pdev = to_platform_device(dev);
-       struct exynos_rng *exynos_rng = platform_get_drvdata(pdev);
-
-       clk_disable_unprepare(exynos_rng->clk);
-
-       return 0;
-}
-
-static int __maybe_unused exynos_rng_runtime_resume(struct device *dev)
-{
-       struct platform_device *pdev = to_platform_device(dev);
-       struct exynos_rng *exynos_rng = platform_get_drvdata(pdev);
-
-       return clk_prepare_enable(exynos_rng->clk);
-}
-
-static int __maybe_unused exynos_rng_suspend(struct device *dev)
-{
-       return pm_runtime_force_suspend(dev);
-}
-
-static int __maybe_unused exynos_rng_resume(struct device *dev)
-{
-       struct platform_device *pdev = to_platform_device(dev);
-       struct exynos_rng *exynos_rng = platform_get_drvdata(pdev);
-       int ret;
-
-       ret = pm_runtime_force_resume(dev);
-       if (ret)
-               return ret;
-
-       return exynos_rng_configure(exynos_rng);
-}
-
-static const struct dev_pm_ops exynos_rng_pm_ops = {
-       SET_SYSTEM_SLEEP_PM_OPS(exynos_rng_suspend, exynos_rng_resume)
-       SET_RUNTIME_PM_OPS(exynos_rng_runtime_suspend,
-                          exynos_rng_runtime_resume, NULL)
-};
-
-static const struct of_device_id exynos_rng_dt_match[] = {
-       {
-               .compatible = "samsung,exynos4-rng",
-       },
-       { },
-};
-MODULE_DEVICE_TABLE(of, exynos_rng_dt_match);
-
-static struct platform_driver exynos_rng_driver = {
-       .driver         = {
-               .name   = "exynos-rng",
-               .pm     = &exynos_rng_pm_ops,
-               .of_match_table = exynos_rng_dt_match,
-       },
-       .probe          = exynos_rng_probe,
-       .remove         = exynos_rng_remove,
-};
-
-module_platform_driver(exynos_rng_driver);
-
-MODULE_DESCRIPTION("EXYNOS 4 H/W Random Number Generator driver");
-MODULE_AUTHOR("Jonghwa Lee <[email protected]>");
-MODULE_LICENSE("GPL");

drivers/crypto/Kconfig +15 -0

index 1a60626937e4..7d1fdf6a751c 100644
@@ -388,6 +388,21 @@ config CRYPTO_DEV_MXC_SCC
          This option enables support for the Security Controller (SCC)
          found in Freescale i.MX25 chips.
 
+config CRYPTO_DEV_EXYNOS_RNG
+       tristate "EXYNOS HW pseudo random number generator support"
+       depends on ARCH_EXYNOS || COMPILE_TEST
+       depends on HAS_IOMEM
+       select CRYPTO_RNG
+       ---help---
+         This driver provides kernel-side support through the
+         cryptographic API for the pseudo random number generator hardware
+         found on Exynos SoCs.
+
+         To compile this driver as a module, choose M here: the
+         module will be called exynos-rng.
+
+         If unsure, say Y.
+
 config CRYPTO_DEV_S5P
        tristate "Support for Samsung S5PV210/Exynos crypto accelerator"
        depends on ARCH_S5PV210 || ARCH_EXYNOS || COMPILE_TEST

drivers/crypto/Makefile +1 -0

index 41ca339e89d3..9603f1862b30 100644
@@ -6,6 +6,7 @@ obj-$(CONFIG_CRYPTO_DEV_CAVIUM_ZIP) += cavium/
 obj-$(CONFIG_CRYPTO_DEV_CCP) += ccp/
 obj-$(CONFIG_CRYPTO_DEV_CHELSIO) += chelsio/
 obj-$(CONFIG_CRYPTO_DEV_CPT) += cavium/cpt/
+obj-$(CONFIG_CRYPTO_DEV_EXYNOS_RNG) += exynos-rng.o
 obj-$(CONFIG_CRYPTO_DEV_FSL_CAAM) += caam/
 obj-$(CONFIG_CRYPTO_DEV_GEODE) += geode-aes.o
 obj-$(CONFIG_CRYPTO_DEV_HIFN_795X) += hifn_795x.o

drivers/crypto/exynos-rng.c new file +51 -0

new file mode 100644
index 000000000000..d657b6243d0a
@@ -0,0 +1,390 @@
+/*
+ * exynos-rng.c - Random Number Generator driver for the Exynos
+ *
+ * Copyright (c) 2017 Krzysztof Kozlowski <[email protected]>
+ *
+ * Loosely based on old driver from drivers/char/hw_random/exynos-rng.c:
+ * Copyright (C) 2012 Samsung Electronics
+ * Jonghwa Lee <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/clk.h>
+#include <linux/crypto.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+#include <crypto/internal/rng.h>
+
+#define EXYNOS_RNG_CONTROL             0x0
+#define EXYNOS_RNG_STATUS              0x10
+#define EXYNOS_RNG_SEED_BASE           0x140
+#define EXYNOS_RNG_SEED(n)             (EXYNOS_RNG_SEED_BASE + (n * 0x4))
+#define EXYNOS_RNG_OUT_BASE            0x160
+#define EXYNOS_RNG_OUT(n)              (EXYNOS_RNG_OUT_BASE + (n * 0x4))
+
+/* EXYNOS_RNG_CONTROL bit fields */
+#define EXYNOS_RNG_CONTROL_START       0x18
+/* EXYNOS_RNG_STATUS bit fields */
+#define EXYNOS_RNG_STATUS_SEED_SETTING_DONE    BIT(1)
+#define EXYNOS_RNG_STATUS_RNG_DONE             BIT(5)
+
+/* Five seed and output registers, each 4 bytes */
+#define EXYNOS_RNG_SEED_REGS           5
+#define EXYNOS_RNG_SEED_SIZE           (EXYNOS_RNG_SEED_REGS * 4)
+
+/*
+ * Driver re-seeds itself with generated random numbers to increase
+ * the randomness.
+ *
+ * Time for next re-seed in ms.
+ */

drivers/crypto/exynos-rng.c new file +7 -0

+static u32 exynos_rng_readl(struct exynos_rng_dev *rng, u32 offset)
+{
+       return readl_relaxed(rng->mem + offset);
+}
+
+static void exynos_rng_writel(struct exynos_rng_dev *rng, u32 val, u32 offset)
+{

drivers/crypto/exynos-rng.c new file +61 -0

+       for (i = 0 ; i < EXYNOS_RNG_SEED_REGS ; i++) {
+               val = seed[i * 4] << 24;
+               val |= seed[i * 4 + 1] << 16;
+               val |= seed[i * 4 + 2] << 8;
+               val |= seed[i * 4 + 3] << 0;
+
+               exynos_rng_writel(rng, val, EXYNOS_RNG_SEED(i));
+       }
+
+       val = exynos_rng_readl(rng, EXYNOS_RNG_STATUS);
+       if (!(val & EXYNOS_RNG_STATUS_SEED_SETTING_DONE)) {
+               dev_warn(rng->dev, "Seed setting not finished\n");
+               return -EIO;
+       }
+
+       rng->last_seeding = jiffies;
+
+       return 0;
+}
+
+/*
+ * Read from output registers and put the data under 'dst' array,
+ * up to dlen bytes.
+ *
+ * Returns number of bytes actually stored in 'dst' (dlen
+ * or EXYNOS_RNG_SEED_SIZE).
+ */
+static unsigned int exynos_rng_copy_random(struct exynos_rng_dev *rng,
+                                          u8 *dst, unsigned int dlen)
+{
+       unsigned int cnt = 0;
+       int i, j;
+       u32 val;
+
+       for (j = 0; j < EXYNOS_RNG_SEED_REGS; j++) {
+               val = exynos_rng_readl(rng, EXYNOS_RNG_OUT(j));
+
+               for (i = 0; i < 4; i++) {
+                       dst[cnt] = val & 0xff;
+                       val >>= 8;
+                       if (++cnt >= dlen)
+                               return cnt;
+               }
+       }
+
+       return cnt;
+}
+
+/*
+ * Start the engine and poll for finish.  Then read from output registers
+ * filling the 'dst' buffer up to 'dlen' bytes or up to size of generated
+ * random data (EXYNOS_RNG_SEED_SIZE).
+ *
+ * On success: return 0 and store number of read bytes under 'read' address.
+ * On error: return -ERRNO.
+ */
+static int exynos_rng_get_random(struct exynos_rng_dev *rng,
+                                u8 *dst, unsigned int dlen,
+                                unsigned int *read)
+{
+       int retry = EXYNOS_RNG_WAIT_RETRIES;

drivers/crypto/exynos-rng.c new file +117 -0

+       /* Clear status bit */
+       exynos_rng_writel(rng, EXYNOS_RNG_STATUS_RNG_DONE,
+                         EXYNOS_RNG_STATUS);
+
+       *read = exynos_rng_copy_random(rng, dst, dlen);
+
+       return 0;
+}
+
+/* Re-seed itself from time to time */
+static void exynos_rng_reseed(struct exynos_rng_dev *rng)
+{
+       unsigned long next_seeding = rng->last_seeding + \
+                                    msecs_to_jiffies(EXYNOS_RNG_RESEED_TIME);
+       unsigned long now = jiffies;
+       u8 seed[EXYNOS_RNG_SEED_SIZE];
+       unsigned int read;
+
+       if (time_before(now, next_seeding))
+               return;
+
+       if (exynos_rng_get_random(rng, seed, sizeof(seed), &read))
+               return;
+
+       exynos_rng_set_seed(rng, seed, read);
+}
+
+static int exynos_rng_generate(struct crypto_rng *tfm,
+                              const u8 *src, unsigned int slen,
+                              u8 *dst, unsigned int dlen)
+{
+       struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
+       struct exynos_rng_dev *rng = ctx->rng;
+       unsigned int read = 0;
+       int ret;
+
+       ret = clk_prepare_enable(rng->clk);
+       if (ret)
+               return ret;
+
+       do {
+               ret = exynos_rng_get_random(rng, dst, dlen, &read);
+               if (ret)
+                       break;
+
+               dlen -= read;
+               dst += read;
+
+               exynos_rng_reseed(rng);
+       } while (dlen > 0);
+
+       clk_disable_unprepare(rng->clk);
+
+       return ret;
+}
+
+static int exynos_rng_seed(struct crypto_rng *tfm, const u8 *seed,
+                          unsigned int slen)
+{
+       struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
+       struct exynos_rng_dev *rng = ctx->rng;
+       int ret;
+
+       ret = clk_prepare_enable(rng->clk);
+       if (ret)
+               return ret;
+
+       ret = exynos_rng_set_seed(ctx->rng, seed, slen);
+
+       clk_disable_unprepare(rng->clk);
+
+       return ret;
+}
+
+static int exynos_rng_kcapi_init(struct crypto_tfm *tfm)
+{
+       struct exynos_rng_ctx *ctx = crypto_tfm_ctx(tfm);
+
+       ctx->rng = exynos_rng_dev;
+
+       return 0;
+}
+
+static struct rng_alg exynos_rng_alg = {
+       .generate               = exynos_rng_generate,
+       .seed                   = exynos_rng_seed,
+       .seedsize               = EXYNOS_RNG_SEED_SIZE,
+       .base                   = {
+               .cra_name               = "exynos_rng",
+               .cra_driver_name        = "exynos_rng",
+               .cra_priority           = 100,
+               .cra_ctxsize            = sizeof(struct exynos_rng_ctx),
+               .cra_module             = THIS_MODULE,
+               .cra_init               = exynos_rng_kcapi_init,
+       }
+};
+
+static int exynos_rng_probe(struct platform_device *pdev)
+{
+       struct exynos_rng_dev *rng;
+       struct resource *res;
+       int ret;
+
+       if (exynos_rng_dev)
+               return -EEXIST;
+
+       rng = devm_kzalloc(&pdev->dev, sizeof(*rng), GFP_KERNEL);
+       if (!rng)
+               return -ENOMEM;
+
+       rng->dev = &pdev->dev;
+       rng->clk = devm_clk_get(&pdev->dev, "secss");
+       if (IS_ERR(rng->clk)) {
+               dev_err(&pdev->dev, "Couldn't get clock.\n");
+               return PTR_ERR(rng->clk);
+       }
+

drivers/crypto/exynos-rng.c new file +4 -0

+       if (ret) {
+               dev_err(&pdev->dev,
+                       "Couldn't register rng crypto alg: %d\n", ret);
+               exynos_rng_dev = NULL;

drivers/crypto/exynos-rng.c new file +76 -1

+       return 0;
+}
+
+static int __maybe_unused exynos_rng_suspend(struct device *dev)
+{
+       struct platform_device *pdev = to_platform_device(dev);
+       struct exynos_rng_dev *rng = platform_get_drvdata(pdev);
+       int ret;
+
+       /* If we were never seeded then after resume it will be the same */
+       if (!rng->last_seeding)
+               return 0;
+
+       rng->seed_save_len = 0;
+       ret = clk_prepare_enable(rng->clk);
+       if (ret)
+               return ret;
+
+       /* Get new random numbers and store them for seeding on resume. */
+       exynos_rng_get_random(rng, rng->seed_save, sizeof(rng->seed_save),
+                             &(rng->seed_save_len));
+       dev_dbg(rng->dev, "Stored %u bytes for seeding on system resume\n",
+               rng->seed_save_len);
+
+       clk_disable_unprepare(rng->clk);
+
+       return 0;
+}
+
+static int __maybe_unused exynos_rng_resume(struct device *dev)
+{
+       struct platform_device *pdev = to_platform_device(dev);
+       struct exynos_rng_dev *rng = platform_get_drvdata(pdev);
+       int ret;
+
+       /* Never seeded so nothing to do */
+       if (!rng->last_seeding)
+               return 0;
+
+       ret = clk_prepare_enable(rng->clk);
+       if (ret)
+               return ret;
+
+       ret = exynos_rng_set_seed(rng, rng->seed_save, rng->seed_save_len);
+
+       clk_disable_unprepare(rng->clk);
+
+       return ret;
+}
+
+static SIMPLE_DEV_PM_OPS(exynos_rng_pm_ops, exynos_rng_suspend,
+                        exynos_rng_resume);
+
+static const struct of_device_id exynos_rng_dt_match[] = {
+       {
+               .compatible = "samsung,exynos4-rng",
+       },
+       { },
+};
+MODULE_DEVICE_TABLE(of, exynos_rng_dt_match);
+
+static struct platform_driver exynos_rng_driver = {
+       .driver         = {
+               .name   = "exynos-rng",
+               .pm     = &exynos_rng_pm_ops,
+               .of_match_table = exynos_rng_dt_match,
+       },
+       .probe          = exynos_rng_probe,
+       .remove         = exynos_rng_remove,
+};
+
+module_platform_driver(exynos_rng_driver);
+
+MODULE_DESCRIPTION("Exynos H/W Random Number Generator driver");
+MODULE_AUTHOR("Krzysztof Kozlowski <[email protected]>");
+MODULE_LICENSE("GPL");
--

2.9.3

.Have some minor comments. Please feel free to correct if I am wrong.

Quoted 430 lines · Krzysztof Kozlowski

Replace existing hw_ranndom/exynos-rng driver with a new, reworked one. This is a driver for pseudo random number generator block which on Exynos4 chipsets must be seeded with some value. On newer Exynos5420 chipsets it might seed itself from true random number generator block but this is not implemented yet.

New driver is a complete rework to use the crypto ALGAPI instead of hw_random API. Rationale for the change:
1. hw_random interface is for true RNG devices.
2. The old driver was seeding itself with jiffies which is not a reliable source for randomness.
3. Device generates five random numbers in each pass but old driver was returning only one thus its performance was reduced.

Compatibility with DeviceTree bindings is preserved.

New driver does not use runtime power management but manually enables and disables the clock when needed. This is preferred approach because using runtime PM just to toggle clock is huge overhead.

Another difference is reseeding itself with generated random data periodically and during resuming from system suspend (previously driver was re-seeding itself again with jiffies).

Signed-off-by Krzysztof Kozlowski <[email protected]>

---
 MAINTAINERS                         |   8 +
 drivers/char/hw_random/Kconfig      |  14 --
 drivers/char/hw_random/Makefile     |   1 -
 drivers/char/hw_random/exynos-rng.c | 231 ---------------------
 drivers/crypto/Kconfig              |  15 ++
 drivers/crypto/Makefile             |   1 +
 drivers/crypto/exynos-rng.c         | 390 ++++++++++++++++++++++++++++++++++++
 7 files changed, 414 insertions(+), 246 deletions(-)
 delete mode 100644 drivers/char/hw_random/exynos-rng.c
 create mode 100644 drivers/crypto/exynos-rng.c

MAINTAINERS +8 -0

index affecc6d59f4..371fda859d43 100644
@@ -10977,6 +10977,14 @@ L:     alsa-devel at alsa-project.org (moderated for non-subscribers)
 S:     Supported
 F:     sound/soc/samsung/
 
+SAMSUNG EXYNOS PSEUDO RANDOM NUMBER GENERATOR (RNG) DRIVER
+M:     Krzysztof Kozlowski <[email protected]>
+L:     linux-crypto at vger.kernel.org
+L:     linux-samsung-soc at vger.kernel.org
+S:     Maintained
+F:     drivers/crypto/exynos-rng.c
+F:     Documentation/devicetree/bindings/rng/samsung,exynos-rng4.txt
+
 SAMSUNG FRAMEBUFFER DRIVER
 M:     Jingoo Han <[email protected]>
 L:     linux-fbdev at vger.kernel.org

drivers/char/hw_random/Kconfig +0 -14

index 0cafe08919c9..bdae802e7154 100644
@@ -294,20 +294,6 @@ config HW_RANDOM_POWERNV
 
          If unsure, say Y.
 
-config HW_RANDOM_EXYNOS
-       tristate "EXYNOS HW random number generator support"
-       depends on ARCH_EXYNOS || COMPILE_TEST
-       depends on HAS_IOMEM
-       default HW_RANDOM
-       ---help---
-         This driver provides kernel-side support for the Random Number
-         Generator hardware found on EXYNOS SOCs.
-
-         To compile this driver as a module, choose M here: the
-         module will be called exynos-rng.
-
-         If unsure, say Y.
-
 config HW_RANDOM_TPM
        tristate "TPM HW Random Number Generator support"
        depends on TCG_TPM

drivers/char/hw_random/Makefile +0 -1

index 5f52b1e4e7be..6f1eecc2045c 100644
@@ -24,7 +24,6 @@ obj-$(CONFIG_HW_RANDOM_OCTEON) += octeon-rng.o
 obj-$(CONFIG_HW_RANDOM_NOMADIK) += nomadik-rng.o
 obj-$(CONFIG_HW_RANDOM_PSERIES) += pseries-rng.o
 obj-$(CONFIG_HW_RANDOM_POWERNV) += powernv-rng.o
-obj-$(CONFIG_HW_RANDOM_EXYNOS) += exynos-rng.o
 obj-$(CONFIG_HW_RANDOM_HISI)   += hisi-rng.o
 obj-$(CONFIG_HW_RANDOM_TPM) += tpm-rng.o
 obj-$(CONFIG_HW_RANDOM_BCM2835) += bcm2835-rng.o

drivers/char/hw_random/exynos-rng.c deleted +0 -231

deleted file mode 100644
index 23d358553b21..000000000000
@@ -1,231 +0,0 @@
-/*
- * exynos-rng.c - Random Number Generator driver for the exynos
- *
- * Copyright (C) 2012 Samsung Electronics
- * Jonghwa Lee <[email protected]>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation;
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
- *
- */
-
-#include <linux/hw_random.h>
-#include <linux/kernel.h>
-#include <linux/module.h>
-#include <linux/io.h>
-#include <linux/platform_device.h>
-#include <linux/clk.h>
-#include <linux/pm_runtime.h>
-#include <linux/err.h>
-
-#define EXYNOS_PRNG_STATUS_OFFSET      0x10
-#define EXYNOS_PRNG_SEED_OFFSET                0x140
-#define EXYNOS_PRNG_OUT1_OFFSET                0x160
-#define SEED_SETTING_DONE              BIT(1)
-#define PRNG_START                     0x18
-#define PRNG_DONE                      BIT(5)
-#define EXYNOS_AUTOSUSPEND_DELAY       100
-
-struct exynos_rng {
-       struct device *dev;
-       struct hwrng rng;
-       void __iomem *mem;
-       struct clk *clk;
-};
-
-static u32 exynos_rng_readl(struct exynos_rng *rng, u32 offset)
-{
-       return  readl_relaxed(rng->mem + offset);
-}
-
-static void exynos_rng_writel(struct exynos_rng *rng, u32 val, u32 offset)
-{
-       writel_relaxed(val, rng->mem + offset);
-}
-
-static int exynos_rng_configure(struct exynos_rng *exynos_rng)
-{
-       int i;
-       int ret = 0;
-
-       for (i = 0 ; i < 5 ; i++)
-               exynos_rng_writel(exynos_rng, jiffies,
-                               EXYNOS_PRNG_SEED_OFFSET + 4*i);
-
-       if (!(exynos_rng_readl(exynos_rng, EXYNOS_PRNG_STATUS_OFFSET)
-                                                & SEED_SETTING_DONE))
-               ret = -EIO;
-
-       return ret;
-}
-
-static int exynos_init(struct hwrng *rng)
-{
-       struct exynos_rng *exynos_rng = container_of(rng,
-                                               struct exynos_rng, rng);
-       int ret = 0;
-
-       pm_runtime_get_sync(exynos_rng->dev);
-       ret = exynos_rng_configure(exynos_rng);
-       pm_runtime_mark_last_busy(exynos_rng->dev);
-       pm_runtime_put_autosuspend(exynos_rng->dev);
-
-       return ret;
-}
-
-static int exynos_read(struct hwrng *rng, void *buf,
-                                       size_t max, bool wait)
-{
-       struct exynos_rng *exynos_rng = container_of(rng,
-                                               struct exynos_rng, rng);
-       u32 *data = buf;
-       int retry = 100;
-       int ret = 4;
-
-       pm_runtime_get_sync(exynos_rng->dev);
-
-       exynos_rng_writel(exynos_rng, PRNG_START, 0);
-
-       while (!(exynos_rng_readl(exynos_rng,
-                       EXYNOS_PRNG_STATUS_OFFSET) & PRNG_DONE) && --retry)
-               cpu_relax();
-       if (!retry) {
-               ret = -ETIMEDOUT;
-               goto out;
-       }
-
-       exynos_rng_writel(exynos_rng, PRNG_DONE, EXYNOS_PRNG_STATUS_OFFSET);
-
-       *data = exynos_rng_readl(exynos_rng, EXYNOS_PRNG_OUT1_OFFSET);
-
-out:
-       pm_runtime_mark_last_busy(exynos_rng->dev);
-       pm_runtime_put_sync_autosuspend(exynos_rng->dev);
-
-       return ret;
-}
-
-static int exynos_rng_probe(struct platform_device *pdev)
-{
-       struct exynos_rng *exynos_rng;
-       struct resource *res;
-       int ret;
-
-       exynos_rng = devm_kzalloc(&pdev->dev, sizeof(struct exynos_rng),
-                                       GFP_KERNEL);
-       if (!exynos_rng)
-               return -ENOMEM;
-
-       exynos_rng->dev = &pdev->dev;
-       exynos_rng->rng.name = "exynos";
-       exynos_rng->rng.init =  exynos_init;
-       exynos_rng->rng.read = exynos_read;
-       exynos_rng->clk = devm_clk_get(&pdev->dev, "secss");
-       if (IS_ERR(exynos_rng->clk)) {
-               dev_err(&pdev->dev, "Couldn't get clock.\n");
-               return -ENOENT;
-       }
-
-       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
-       exynos_rng->mem = devm_ioremap_resource(&pdev->dev, res);
-       if (IS_ERR(exynos_rng->mem))
-               return PTR_ERR(exynos_rng->mem);
-
-       platform_set_drvdata(pdev, exynos_rng);
-
-       pm_runtime_set_autosuspend_delay(&pdev->dev, EXYNOS_AUTOSUSPEND_DELAY);
-       pm_runtime_use_autosuspend(&pdev->dev);
-       pm_runtime_enable(&pdev->dev);
-
-       ret = devm_hwrng_register(&pdev->dev, &exynos_rng->rng);
-       if (ret) {
-               pm_runtime_dont_use_autosuspend(&pdev->dev);
-               pm_runtime_disable(&pdev->dev);
-       }
-
-       return ret;
-}
-
-static int exynos_rng_remove(struct platform_device *pdev)
-{
-       pm_runtime_dont_use_autosuspend(&pdev->dev);
-       pm_runtime_disable(&pdev->dev);
-
-       return 0;
-}
-
-static int __maybe_unused exynos_rng_runtime_suspend(struct device *dev)
-{
-       struct platform_device *pdev = to_platform_device(dev);
-       struct exynos_rng *exynos_rng = platform_get_drvdata(pdev);
-
-       clk_disable_unprepare(exynos_rng->clk);
-
-       return 0;
-}
-
-static int __maybe_unused exynos_rng_runtime_resume(struct device *dev)
-{
-       struct platform_device *pdev = to_platform_device(dev);
-       struct exynos_rng *exynos_rng = platform_get_drvdata(pdev);
-
-       return clk_prepare_enable(exynos_rng->clk);
-}
-
-static int __maybe_unused exynos_rng_suspend(struct device *dev)
-{
-       return pm_runtime_force_suspend(dev);
-}
-
-static int __maybe_unused exynos_rng_resume(struct device *dev)
-{
-       struct platform_device *pdev = to_platform_device(dev);
-       struct exynos_rng *exynos_rng = platform_get_drvdata(pdev);
-       int ret;
-
-       ret = pm_runtime_force_resume(dev);
-       if (ret)
-               return ret;
-
-       return exynos_rng_configure(exynos_rng);
-}
-
-static const struct dev_pm_ops exynos_rng_pm_ops = {
-       SET_SYSTEM_SLEEP_PM_OPS(exynos_rng_suspend, exynos_rng_resume)
-       SET_RUNTIME_PM_OPS(exynos_rng_runtime_suspend,
-                          exynos_rng_runtime_resume, NULL)
-};
-
-static const struct of_device_id exynos_rng_dt_match[] = {
-       {
-               .compatible = "samsung,exynos4-rng",
-       },
-       { },
-};
-MODULE_DEVICE_TABLE(of, exynos_rng_dt_match);
-
-static struct platform_driver exynos_rng_driver = {
-       .driver         = {
-               .name   = "exynos-rng",
-               .pm     = &exynos_rng_pm_ops,
-               .of_match_table = exynos_rng_dt_match,
-       },
-       .probe          = exynos_rng_probe,
-       .remove         = exynos_rng_remove,
-};
-
-module_platform_driver(exynos_rng_driver);
-
-MODULE_DESCRIPTION("EXYNOS 4 H/W Random Number Generator driver");
-MODULE_AUTHOR("Jonghwa Lee <[email protected]>");
-MODULE_LICENSE("GPL");

drivers/crypto/Kconfig +15 -0

index 1a60626937e4..7d1fdf6a751c 100644
@@ -388,6 +388,21 @@ config CRYPTO_DEV_MXC_SCC
          This option enables support for the Security Controller (SCC)
          found in Freescale i.MX25 chips.
 
+config CRYPTO_DEV_EXYNOS_RNG
+       tristate "EXYNOS HW pseudo random number generator support"
+       depends on ARCH_EXYNOS || COMPILE_TEST
+       depends on HAS_IOMEM
+       select CRYPTO_RNG
+       ---help---
+         This driver provides kernel-side support through the
+         cryptographic API for the pseudo random number generator hardware
+         found on Exynos SoCs.
+
+         To compile this driver as a module, choose M here: the
+         module will be called exynos-rng.
+
+         If unsure, say Y.
+
 config CRYPTO_DEV_S5P
        tristate "Support for Samsung S5PV210/Exynos crypto accelerator"
        depends on ARCH_S5PV210 || ARCH_EXYNOS || COMPILE_TEST

drivers/crypto/Makefile +1 -0

index 41ca339e89d3..9603f1862b30 100644
@@ -6,6 +6,7 @@ obj-$(CONFIG_CRYPTO_DEV_CAVIUM_ZIP) += cavium/
 obj-$(CONFIG_CRYPTO_DEV_CCP) += ccp/
 obj-$(CONFIG_CRYPTO_DEV_CHELSIO) += chelsio/
 obj-$(CONFIG_CRYPTO_DEV_CPT) += cavium/cpt/
+obj-$(CONFIG_CRYPTO_DEV_EXYNOS_RNG) += exynos-rng.o
 obj-$(CONFIG_CRYPTO_DEV_FSL_CAAM) += caam/
 obj-$(CONFIG_CRYPTO_DEV_GEODE) += geode-aes.o
 obj-$(CONFIG_CRYPTO_DEV_HIFN_795X) += hifn_795x.o

drivers/crypto/exynos-rng.c new file +55 -0

new file mode 100644
index 000000000000..d657b6243d0a
@@ -0,0 +1,390 @@
+/*
+ * exynos-rng.c - Random Number Generator driver for the Exynos
+ *
+ * Copyright (c) 2017 Krzysztof Kozlowski <[email protected]>
+ *
+ * Loosely based on old driver from drivers/char/hw_random/exynos-rng.c:
+ * Copyright (C) 2012 Samsung Electronics
+ * Jonghwa Lee <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/clk.h>
+#include <linux/crypto.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+#include <crypto/internal/rng.h>
+
+#define EXYNOS_RNG_CONTROL             0x0
+#define EXYNOS_RNG_STATUS              0x10
+#define EXYNOS_RNG_SEED_BASE           0x140
+#define EXYNOS_RNG_SEED(n)             (EXYNOS_RNG_SEED_BASE + (n * 0x4))
+#define EXYNOS_RNG_OUT_BASE            0x160
+#define EXYNOS_RNG_OUT(n)              (EXYNOS_RNG_OUT_BASE + (n * 0x4))
+
+/* EXYNOS_RNG_CONTROL bit fields */
+#define EXYNOS_RNG_CONTROL_START       0x18
+/* EXYNOS_RNG_STATUS bit fields */
+#define EXYNOS_RNG_STATUS_SEED_SETTING_DONE    BIT(1)
+#define EXYNOS_RNG_STATUS_RNG_DONE             BIT(5)
+
+/* Five seed and output registers, each 4 bytes */
+#define EXYNOS_RNG_SEED_REGS           5
+#define EXYNOS_RNG_SEED_SIZE           (EXYNOS_RNG_SEED_REGS * 4)
+
+/*
+ * Driver re-seeds itself with generated random numbers to increase
+ * the randomness.
+ *
+ * Time for next re-seed in ms.
+ */
+#define EXYNOS_RNG_RESEED_TIME         100
+/*
+ * In polling mode, do not wait infinitely for the engine to finish the work.
+ */

drivers/crypto/exynos-rng.c line 61

Quoted 6 lines

drivers/crypto/exynos-rng.c new file +6 -0

+#define EXYNOS_RNG_WAIT_RETRIES                100
+
+/* Context for crypto */
+struct exynos_rng_ctx {
+       struct exynos_rng_dev           *rng;
+};

Is exynos_rng_ctx really necessary? Can't exynos_rng_dev be used directly?

Quoted 6 lines

drivers/crypto/exynos-rng.c new file +6 -0

+/* Device associated memory */
+struct exynos_rng_dev {
+       struct device                   *dev;
+       struct exynos_rng_ctx           *ctx;
+       void __iomem                    *mem;
+       struct clk                      *clk;

drivers/crypto/exynos-rng.c line 74

Quoted 6 lines

drivers/crypto/exynos-rng.c new file +6 -0

+       /* Generated numbers stored for seeding during resume */
+       u8                              seed_save[EXYNOS_RNG_SEED_SIZE];
+       unsigned int                    seed_save_len;
+       /* Time of last seeding in jiffies */
+       unsigned long                   last_seeding;
+};

Wondering if storing 'ctx' is really necessary. Can that be eliminated?

drivers/crypto/exynos-rng.c line 76

Quoted 1 line

drivers/crypto/exynos-rng.c new file +1 -0

+static struct exynos_rng_dev *exynos_rng_dev;

Having an instance of exynos_rng_dev makes this driver to work with only 1 rng hardware block. Is this desired?

Also having an instance of exynos_rng_dev seems unnecessary. Can it be removed?

Quoted 12 lines

drivers/crypto/exynos-rng.c new file +11 -0

+static u32 exynos_rng_readl(struct exynos_rng_dev *rng, u32 offset)
+{
+       return readl_relaxed(rng->mem + offset);
+}
+
+static void exynos_rng_writel(struct exynos_rng_dev *rng, u32 val, u32 offset)
+{
+       writel_relaxed(val, rng->mem + offset);
+}
+
+static int exynos_rng_set_seed(struct exynos_rng_dev *rng,

drivers/crypto/exynos-rng.c line 94

Quoted 6 lines

drivers/crypto/exynos-rng.c new file +6 -0

+                              const u8 *seed, unsigned int slen)
+{
+       u32 val;
+       int i;
+
+       dev_dbg(rng->dev, "Seeding with %u bytes\n", slen);

This log can be put after the 'slen < EXYNOS_RNG_SEED_SIZE' condition check.

drivers/crypto/exynos-rng.c line 99

Quoted 5 lines

drivers/crypto/exynos-rng.c new file +4 -0

+       if (slen < EXYNOS_RNG_SEED_SIZE) {
+               dev_warn(rng->dev, "Seed too short (only %u bytes)\n", slen);
+               return -EINVAL;
+       }

Will it be helpful to print the required seed size?

Also wondering if the seed size check is required as it is given as a parameter while registering with crypto framework.

Quoted 69 lines

drivers/crypto/exynos-rng.c new file +68 -0

+       for (i = 0 ; i < EXYNOS_RNG_SEED_REGS ; i++) {
+               val = seed[i * 4] << 24;
+               val |= seed[i * 4 + 1] << 16;
+               val |= seed[i * 4 + 2] << 8;
+               val |= seed[i * 4 + 3] << 0;
+
+               exynos_rng_writel(rng, val, EXYNOS_RNG_SEED(i));
+       }
+
+       val = exynos_rng_readl(rng, EXYNOS_RNG_STATUS);
+       if (!(val & EXYNOS_RNG_STATUS_SEED_SETTING_DONE)) {
+               dev_warn(rng->dev, "Seed setting not finished\n");
+               return -EIO;
+       }
+
+       rng->last_seeding = jiffies;
+
+       return 0;
+}
+
+/*
+ * Read from output registers and put the data under 'dst' array,
+ * up to dlen bytes.
+ *
+ * Returns number of bytes actually stored in 'dst' (dlen
+ * or EXYNOS_RNG_SEED_SIZE).
+ */
+static unsigned int exynos_rng_copy_random(struct exynos_rng_dev *rng,
+                                          u8 *dst, unsigned int dlen)
+{
+       unsigned int cnt = 0;
+       int i, j;
+       u32 val;
+
+       for (j = 0; j < EXYNOS_RNG_SEED_REGS; j++) {
+               val = exynos_rng_readl(rng, EXYNOS_RNG_OUT(j));
+
+               for (i = 0; i < 4; i++) {
+                       dst[cnt] = val & 0xff;
+                       val >>= 8;
+                       if (++cnt >= dlen)
+                               return cnt;
+               }
+       }
+
+       return cnt;
+}
+
+/*
+ * Start the engine and poll for finish.  Then read from output registers
+ * filling the 'dst' buffer up to 'dlen' bytes or up to size of generated
+ * random data (EXYNOS_RNG_SEED_SIZE).
+ *
+ * On success: return 0 and store number of read bytes under 'read' address.
+ * On error: return -ERRNO.
+ */
+static int exynos_rng_get_random(struct exynos_rng_dev *rng,
+                                u8 *dst, unsigned int dlen,
+                                unsigned int *read)
+{
+       int retry = EXYNOS_RNG_WAIT_RETRIES;
+
+       exynos_rng_writel(rng, EXYNOS_RNG_CONTROL_START,
+                         EXYNOS_RNG_CONTROL);
+
+       while (!(exynos_rng_readl(rng,
+                       EXYNOS_RNG_STATUS) & EXYNOS_RNG_STATUS_RNG_DONE) && --retry)
+               cpu_relax();

drivers/crypto/exynos-rng.c line 171

Quoted 3 lines

drivers/crypto/exynos-rng.c new file +3 -0

+
+       if (!retry)
+               return -ETIMEDOUT;

What would happen if the RNG block could not calculate data within the timeout but did calculate random data after the timeout? In that case the status bit would not have not been cleared. Will that cause an issue?

Quoted 123 lines

drivers/crypto/exynos-rng.c new file +122 -0

+       /* Clear status bit */
+       exynos_rng_writel(rng, EXYNOS_RNG_STATUS_RNG_DONE,
+                         EXYNOS_RNG_STATUS);
+
+       *read = exynos_rng_copy_random(rng, dst, dlen);
+
+       return 0;
+}
+
+/* Re-seed itself from time to time */
+static void exynos_rng_reseed(struct exynos_rng_dev *rng)
+{
+       unsigned long next_seeding = rng->last_seeding + \
+                                    msecs_to_jiffies(EXYNOS_RNG_RESEED_TIME);
+       unsigned long now = jiffies;
+       u8 seed[EXYNOS_RNG_SEED_SIZE];
+       unsigned int read;
+
+       if (time_before(now, next_seeding))
+               return;
+
+       if (exynos_rng_get_random(rng, seed, sizeof(seed), &read))
+               return;
+
+       exynos_rng_set_seed(rng, seed, read);
+}
+
+static int exynos_rng_generate(struct crypto_rng *tfm,
+                              const u8 *src, unsigned int slen,
+                              u8 *dst, unsigned int dlen)
+{
+       struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
+       struct exynos_rng_dev *rng = ctx->rng;
+       unsigned int read = 0;
+       int ret;
+
+       ret = clk_prepare_enable(rng->clk);
+       if (ret)
+               return ret;
+
+       do {
+               ret = exynos_rng_get_random(rng, dst, dlen, &read);
+               if (ret)
+                       break;
+
+               dlen -= read;
+               dst += read;
+
+               exynos_rng_reseed(rng);
+       } while (dlen > 0);
+
+       clk_disable_unprepare(rng->clk);
+
+       return ret;
+}
+
+static int exynos_rng_seed(struct crypto_rng *tfm, const u8 *seed,
+                          unsigned int slen)
+{
+       struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
+       struct exynos_rng_dev *rng = ctx->rng;
+       int ret;
+
+       ret = clk_prepare_enable(rng->clk);
+       if (ret)
+               return ret;
+
+       ret = exynos_rng_set_seed(ctx->rng, seed, slen);
+
+       clk_disable_unprepare(rng->clk);
+
+       return ret;
+}
+
+static int exynos_rng_kcapi_init(struct crypto_tfm *tfm)
+{
+       struct exynos_rng_ctx *ctx = crypto_tfm_ctx(tfm);
+
+       ctx->rng = exynos_rng_dev;
+
+       return 0;
+}
+
+static struct rng_alg exynos_rng_alg = {
+       .generate               = exynos_rng_generate,
+       .seed                   = exynos_rng_seed,
+       .seedsize               = EXYNOS_RNG_SEED_SIZE,
+       .base                   = {
+               .cra_name               = "exynos_rng",
+               .cra_driver_name        = "exynos_rng",
+               .cra_priority           = 100,
+               .cra_ctxsize            = sizeof(struct exynos_rng_ctx),
+               .cra_module             = THIS_MODULE,
+               .cra_init               = exynos_rng_kcapi_init,
+       }
+};
+
+static int exynos_rng_probe(struct platform_device *pdev)
+{
+       struct exynos_rng_dev *rng;
+       struct resource *res;
+       int ret;
+
+       if (exynos_rng_dev)
+               return -EEXIST;
+
+       rng = devm_kzalloc(&pdev->dev, sizeof(*rng), GFP_KERNEL);
+       if (!rng)
+               return -ENOMEM;
+
+       rng->dev = &pdev->dev;
+       rng->clk = devm_clk_get(&pdev->dev, "secss");
+       if (IS_ERR(rng->clk)) {
+               dev_err(&pdev->dev, "Couldn't get clock.\n");
+               return PTR_ERR(rng->clk);
+       }
+
+       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+       rng->mem = devm_ioremap_resource(&pdev->dev, res);
+       if (IS_ERR(rng->mem))
+               return PTR_ERR(rng->mem);
+

drivers/crypto/exynos-rng.c line 299

Quoted 5 lines

drivers/crypto/exynos-rng.c new file +5 -0

+       platform_set_drvdata(pdev, rng);
+
+       exynos_rng_dev = rng;
+
+       ret = crypto_register_rng(&exynos_rng_alg);

Do you mind adding devm_crypto_register_rng? If added the .remove method will become unnecessary and error handling code can be removed.

Quoted 5 lines

drivers/crypto/exynos-rng.c new file +4 -0

+       if (ret) {
+               dev_err(&pdev->dev,
+                       "Couldn't register rng crypto alg: %d\n", ret);
+               exynos_rng_dev = NULL;

drivers/crypto/exynos-rng.c line 313

Quoted 10 lines

drivers/crypto/exynos-rng.c new file +10 -0

+       }
+
+       return ret;
+}
+
+static int exynos_rng_remove(struct platform_device *pdev)
+{
+       crypto_unregister_rng(&exynos_rng_alg);
+
+       exynos_rng_dev = NULL;

This looks unnecessary as the module is unloading.

Quoted 6 lines

Quoted 4 lines

(quoted diff) +2 -0

+       if (slen < EXYNOS_RNG_SEED_SIZE) {
+               dev_warn(rng->dev, "Seed too short (only %u bytes)\n",

slen); + return -EINVAL;
+ }

Will it be helpful to print the required seed size?

It is in /proc/crypto... It is not a problem to print it but isn't that redundant?

Quoted 64 lines · PrasannaKumar Muralidharan

.Have some minor comments. Please feel free to correct if I am wrong.

Quoted 61 lines · Krzysztof Kozlowski

drivers/crypto/exynos-rng.c new file +55 -0

new file mode 100644
index 000000000000..d657b6243d0a
@@ -0,0 +1,390 @@
+/*
+ * exynos-rng.c - Random Number Generator driver for the Exynos
+ *
+ * Copyright (c) 2017 Krzysztof Kozlowski <[email protected]>
+ *
+ * Loosely based on old driver from drivers/char/hw_random/exynos-rng.c:
+ * Copyright (C) 2012 Samsung Electronics
+ * Jonghwa Lee <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/clk.h>
+#include <linux/crypto.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+#include <crypto/internal/rng.h>
+
+#define EXYNOS_RNG_CONTROL             0x0
+#define EXYNOS_RNG_STATUS              0x10
+#define EXYNOS_RNG_SEED_BASE           0x140
+#define EXYNOS_RNG_SEED(n)             (EXYNOS_RNG_SEED_BASE + (n * 0x4))
+#define EXYNOS_RNG_OUT_BASE            0x160
+#define EXYNOS_RNG_OUT(n)              (EXYNOS_RNG_OUT_BASE + (n * 0x4))
+
+/* EXYNOS_RNG_CONTROL bit fields */
+#define EXYNOS_RNG_CONTROL_START       0x18
+/* EXYNOS_RNG_STATUS bit fields */
+#define EXYNOS_RNG_STATUS_SEED_SETTING_DONE    BIT(1)
+#define EXYNOS_RNG_STATUS_RNG_DONE             BIT(5)
+
+/* Five seed and output registers, each 4 bytes */
+#define EXYNOS_RNG_SEED_REGS           5
+#define EXYNOS_RNG_SEED_SIZE           (EXYNOS_RNG_SEED_REGS * 4)
+
+/*
+ * Driver re-seeds itself with generated random numbers to increase
+ * the randomness.
+ *
+ * Time for next re-seed in ms.
+ */
+#define EXYNOS_RNG_RESEED_TIME         100
+/*
+ * In polling mode, do not wait infinitely for the engine to finish the work.
+ */

Quoted 9 lines

drivers/crypto/exynos-rng.c line 61

Quoted 6 lines

drivers/crypto/exynos-rng.c new file +6 -0

+#define EXYNOS_RNG_WAIT_RETRIES                100
+
+/* Context for crypto */
+struct exynos_rng_ctx {
+       struct exynos_rng_dev           *rng;
+};

Is exynos_rng_ctx really necessary? Can't exynos_rng_dev be used directly?

I couldn't find a way to pass an instance of exynos_rng_dev to generate() and seed() calls.

Quoted 6 lines

Quoted 6 lines

drivers/crypto/exynos-rng.c new file +6 -0

+/* Device associated memory */
+struct exynos_rng_dev {
+       struct device                   *dev;
+       struct exynos_rng_ctx           *ctx;
+       void __iomem                    *mem;
+       struct clk                      *clk;

Quoted 8 lines

drivers/crypto/exynos-rng.c line 74

Quoted 6 lines

drivers/crypto/exynos-rng.c new file +6 -0

+       /* Generated numbers stored for seeding during resume */
+       u8                              seed_save[EXYNOS_RNG_SEED_SIZE];
+       unsigned int                    seed_save_len;
+       /* Time of last seeding in jiffies */
+       unsigned long                   last_seeding;
+};

Wondering if storing 'ctx' is really necessary. Can that be eliminated?

Yes, it can.

Quoted 4 lines

drivers/crypto/exynos-rng.c line 76

Quoted 1 line

drivers/crypto/exynos-rng.c new file +1 -0

+static struct exynos_rng_dev *exynos_rng_dev;

Having an instance of exynos_rng_dev makes this driver to work with only 1 rng hardware block. Is this desired?

First of all, there is only one hardware block. ioremap_resource also ensures that. Second of all, how would you like to pass the platform device specific data to crypto calls?

Quoted 1 line

Also having an instance of exynos_rng_dev seems unnecessary. Can it be removed?

Why do you think it is unnecessary?

Quoted 12 lines

Quoted 12 lines

drivers/crypto/exynos-rng.c new file +11 -0

+static u32 exynos_rng_readl(struct exynos_rng_dev *rng, u32 offset)
+{
+       return readl_relaxed(rng->mem + offset);
+}
+
+static void exynos_rng_writel(struct exynos_rng_dev *rng, u32 val, u32 offset)
+{
+       writel_relaxed(val, rng->mem + offset);
+}
+
+static int exynos_rng_set_seed(struct exynos_rng_dev *rng,

Quoted 8 lines

drivers/crypto/exynos-rng.c line 94

Quoted 6 lines

drivers/crypto/exynos-rng.c new file +6 -0

+                              const u8 *seed, unsigned int slen)
+{
+       u32 val;
+       int i;
+
+       dev_dbg(rng->dev, "Seeding with %u bytes\n", slen);

This log can be put after the 'slen < EXYNOS_RNG_SEED_SIZE' condition check.

It can be put there but what is the benefit? The purpose of this log was to show the start of seeding so the beginning of function seems very natural to me.

Quoted 6 lines

Quoted 5 lines

drivers/crypto/exynos-rng.c new file +4 -0

+       if (slen < EXYNOS_RNG_SEED_SIZE) {
+               dev_warn(rng->dev, "Seed too short (only %u bytes)\n", slen);
+               return -EINVAL;
+       }

Quoted 1 line

Will it be helpful to print the required seed size?

It is in /proc/crypto... It is not a problem to print it but isn't that redundant?

Quoted 3 lines

Also wondering if the seed size check is required as it is given as a parameter while registering with crypto framework.

Still the framework might pass something smaller but the size is a strict requirement by the code below and by the HW engine.

Quoted 69 lines

Quoted 69 lines

drivers/crypto/exynos-rng.c new file +68 -0

+       for (i = 0 ; i < EXYNOS_RNG_SEED_REGS ; i++) {
+               val = seed[i * 4] << 24;
+               val |= seed[i * 4 + 1] << 16;
+               val |= seed[i * 4 + 2] << 8;
+               val |= seed[i * 4 + 3] << 0;
+
+               exynos_rng_writel(rng, val, EXYNOS_RNG_SEED(i));
+       }
+
+       val = exynos_rng_readl(rng, EXYNOS_RNG_STATUS);
+       if (!(val & EXYNOS_RNG_STATUS_SEED_SETTING_DONE)) {
+               dev_warn(rng->dev, "Seed setting not finished\n");
+               return -EIO;
+       }
+
+       rng->last_seeding = jiffies;
+
+       return 0;
+}
+
+/*
+ * Read from output registers and put the data under 'dst' array,
+ * up to dlen bytes.
+ *
+ * Returns number of bytes actually stored in 'dst' (dlen
+ * or EXYNOS_RNG_SEED_SIZE).
+ */
+static unsigned int exynos_rng_copy_random(struct exynos_rng_dev *rng,
+                                          u8 *dst, unsigned int dlen)
+{
+       unsigned int cnt = 0;
+       int i, j;
+       u32 val;
+
+       for (j = 0; j < EXYNOS_RNG_SEED_REGS; j++) {
+               val = exynos_rng_readl(rng, EXYNOS_RNG_OUT(j));
+
+               for (i = 0; i < 4; i++) {
+                       dst[cnt] = val & 0xff;
+                       val >>= 8;
+                       if (++cnt >= dlen)
+                               return cnt;
+               }
+       }
+
+       return cnt;
+}
+
+/*
+ * Start the engine and poll for finish.  Then read from output registers
+ * filling the 'dst' buffer up to 'dlen' bytes or up to size of generated
+ * random data (EXYNOS_RNG_SEED_SIZE).
+ *
+ * On success: return 0 and store number of read bytes under 'read' address.
+ * On error: return -ERRNO.
+ */
+static int exynos_rng_get_random(struct exynos_rng_dev *rng,
+                                u8 *dst, unsigned int dlen,
+                                unsigned int *read)
+{
+       int retry = EXYNOS_RNG_WAIT_RETRIES;
+
+       exynos_rng_writel(rng, EXYNOS_RNG_CONTROL_START,
+                         EXYNOS_RNG_CONTROL);
+
+       while (!(exynos_rng_readl(rng,
+                       EXYNOS_RNG_STATUS) & EXYNOS_RNG_STATUS_RNG_DONE) && --retry)
+               cpu_relax();

Quoted 8 lines

drivers/crypto/exynos-rng.c line 171

Quoted 3 lines

drivers/crypto/exynos-rng.c new file +3 -0

+
+       if (!retry)
+               return -ETIMEDOUT;

What would happen if the RNG block could not calculate data within the timeout but did calculate random data after the timeout? In that case the status bit would not have not been cleared. Will that cause an issue?

In such case we do not have control over it anyway. If HW does not work, then driver cannot fix it. I am not sure how would you want to handle such case?

Quoted 123 lines

Quoted 123 lines

drivers/crypto/exynos-rng.c new file +122 -0

+       /* Clear status bit */
+       exynos_rng_writel(rng, EXYNOS_RNG_STATUS_RNG_DONE,
+                         EXYNOS_RNG_STATUS);
+
+       *read = exynos_rng_copy_random(rng, dst, dlen);
+
+       return 0;
+}
+
+/* Re-seed itself from time to time */
+static void exynos_rng_reseed(struct exynos_rng_dev *rng)
+{
+       unsigned long next_seeding = rng->last_seeding + \
+                                    msecs_to_jiffies(EXYNOS_RNG_RESEED_TIME);
+       unsigned long now = jiffies;
+       u8 seed[EXYNOS_RNG_SEED_SIZE];
+       unsigned int read;
+
+       if (time_before(now, next_seeding))
+               return;
+
+       if (exynos_rng_get_random(rng, seed, sizeof(seed), &read))
+               return;
+
+       exynos_rng_set_seed(rng, seed, read);
+}
+
+static int exynos_rng_generate(struct crypto_rng *tfm,
+                              const u8 *src, unsigned int slen,
+                              u8 *dst, unsigned int dlen)
+{
+       struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
+       struct exynos_rng_dev *rng = ctx->rng;
+       unsigned int read = 0;
+       int ret;
+
+       ret = clk_prepare_enable(rng->clk);
+       if (ret)
+               return ret;
+
+       do {
+               ret = exynos_rng_get_random(rng, dst, dlen, &read);
+               if (ret)
+                       break;
+
+               dlen -= read;
+               dst += read;
+
+               exynos_rng_reseed(rng);
+       } while (dlen > 0);
+
+       clk_disable_unprepare(rng->clk);
+
+       return ret;
+}
+
+static int exynos_rng_seed(struct crypto_rng *tfm, const u8 *seed,
+                          unsigned int slen)
+{
+       struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
+       struct exynos_rng_dev *rng = ctx->rng;
+       int ret;
+
+       ret = clk_prepare_enable(rng->clk);
+       if (ret)
+               return ret;
+
+       ret = exynos_rng_set_seed(ctx->rng, seed, slen);
+
+       clk_disable_unprepare(rng->clk);
+
+       return ret;
+}
+
+static int exynos_rng_kcapi_init(struct crypto_tfm *tfm)
+{
+       struct exynos_rng_ctx *ctx = crypto_tfm_ctx(tfm);
+
+       ctx->rng = exynos_rng_dev;
+
+       return 0;
+}
+
+static struct rng_alg exynos_rng_alg = {
+       .generate               = exynos_rng_generate,
+       .seed                   = exynos_rng_seed,
+       .seedsize               = EXYNOS_RNG_SEED_SIZE,
+       .base                   = {
+               .cra_name               = "exynos_rng",
+               .cra_driver_name        = "exynos_rng",
+               .cra_priority           = 100,
+               .cra_ctxsize            = sizeof(struct exynos_rng_ctx),
+               .cra_module             = THIS_MODULE,
+               .cra_init               = exynos_rng_kcapi_init,
+       }
+};
+
+static int exynos_rng_probe(struct platform_device *pdev)
+{
+       struct exynos_rng_dev *rng;
+       struct resource *res;
+       int ret;
+
+       if (exynos_rng_dev)
+               return -EEXIST;
+
+       rng = devm_kzalloc(&pdev->dev, sizeof(*rng), GFP_KERNEL);
+       if (!rng)
+               return -ENOMEM;
+
+       rng->dev = &pdev->dev;
+       rng->clk = devm_clk_get(&pdev->dev, "secss");
+       if (IS_ERR(rng->clk)) {
+               dev_err(&pdev->dev, "Couldn't get clock.\n");
+               return PTR_ERR(rng->clk);
+       }
+
+       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+       rng->mem = devm_ioremap_resource(&pdev->dev, res);
+       if (IS_ERR(rng->mem))
+               return PTR_ERR(rng->mem);
+

Quoted 8 lines

drivers/crypto/exynos-rng.c line 299

Quoted 5 lines

drivers/crypto/exynos-rng.c new file +5 -0

+       platform_set_drvdata(pdev, rng);
+
+       exynos_rng_dev = rng;
+
+       ret = crypto_register_rng(&exynos_rng_alg);

Do you mind adding devm_crypto_register_rng? If added the .remove method will become unnecessary and error handling code can be removed.

There is no devm_crypto_register_rng(). First it would have to be added. That is out of scope of this patch.

Quoted 17 lines

Quoted 5 lines

drivers/crypto/exynos-rng.c new file +4 -0

+       if (ret) {
+               dev_err(&pdev->dev,
+                       "Couldn't register rng crypto alg: %d\n", ret);
+               exynos_rng_dev = NULL;

drivers/crypto/exynos-rng.c line 313

Quoted 10 lines

drivers/crypto/exynos-rng.c new file +10 -0

+       }
+
+       return ret;
+}
+
+static int exynos_rng_remove(struct platform_device *pdev)
+{
+       crypto_unregister_rng(&exynos_rng_alg);
+
+       exynos_rng_dev = NULL;

This looks unnecessary as the module is unloading.

I think it is necessary, because remove is called on unbind. Re-binding a device will not cause static memory to be initialized.

Quoted 9 lines

Quoted 6 lines

Quoted 4 lines

(quoted diff) +2 -0

+       if (slen < EXYNOS_RNG_SEED_SIZE) {
+               dev_warn(rng->dev, "Seed too short (only %u bytes)\n",

slen); + return -EINVAL;
+ }

Will it be helpful to print the required seed size?

It is in /proc/crypto... It is not a problem to print it but isn't that redundant?

Not necessary if it is already available.

Am Sonntag, 26. M?rz 2017, 18:46:02 CEST schrieb PrasannaKumar Muralidharan:

Hi Krzysztof,

Quoted 7 lines

Quoted 7 lines

Quoted 6 lines

Quoted 4 lines

(quoted diff) +2 -0

+       if (slen < EXYNOS_RNG_SEED_SIZE) {
+               dev_warn(rng->dev, "Seed too short (only %u bytes)\n",

slen); + return -EINVAL;
+ }

Will it be helpful to print the required seed size?

Quoted 4 lines

Quoted 2 lines

It is in /proc/crypto... It is not a problem to print it but isn't that redundant?

Not necessary if it is already available.

Maybe the dev_warn should be removed. Note, unprivileged user space can trigger this warning by simply invoking the seeding operation over and over again with an insufficient seed size. This would clutter the log.

drivers/crypto/exynos-rng.c new file +11 -0

+static int exynos_rng_set_seed(struct exynos_rng_dev *rng,
+			       const u8 *seed, unsigned int slen)
+{
+	u32 val;
+	int i;
+
+	dev_dbg(rng->dev, "Seeding with %u bytes\n", slen);
+
+	if (slen < EXYNOS_RNG_SEED_SIZE) {
+		dev_warn(rng->dev, "Seed too short (only %u bytes)\n", slen);
+		return -EINVAL;

Am Samstag, 25. M?rz 2017, 17:26:52 CEST schrieb Krzysztof Kozlowski:

Quoted 20 lines

drivers/crypto/exynos-rng.c new file +20 -0

+static int exynos_rng_set_seed(struct exynos_rng_dev *rng,
+			       const u8 *seed, unsigned int slen)
+{
+	u32 val;
+	int i;
+
+	dev_dbg(rng->dev, "Seeding with %u bytes\n", slen);
+
+	if (slen < EXYNOS_RNG_SEED_SIZE) {
+		dev_warn(rng->dev, "Seed too short (only %u bytes)\n", slen);
+		return -EINVAL;
+	}
+
+	for (i = 0 ; i < EXYNOS_RNG_SEED_REGS ; i++) {
+		val = seed[i * 4] << 24;
+		val |= seed[i * 4 + 1] << 16;
+		val |= seed[i * 4 + 2] << 8;
+		val |= seed[i * 4 + 3] << 0;
+
+		exynos_rng_writel(rng, val, EXYNOS_RNG_SEED(i));

Review

Quoted 1 line

(quoted diff) +1 -0

+	}

Would it make sense to add another outer loop here to allow all of slen to be injected into the DRNG? Note, in some cases, a user wants to add more seed into the DRNG than the actual seed size. In this case, the DRNG acts as a compression operation of entropy. This is used when the entropy-to-data ratio is not 1:1. In a lot of cases, users have a seed which has less entropy in bits per data bit.

Quoted 6 lines

Would it make sense to add another outer loop here to allow all of slen to be injected into the DRNG? Note, in some cases, a user wants to add more seed into the DRNG than the actual seed size. In this case, the DRNG acts as a compression operation of entropy. This is used when the entropy-to-data ratio is not 1:1. In a lot of cases, users have a seed which has less entropy in bits per data bit.

Hi,

I do not know whether this would have any benefit on hardware. The datasheet is not describing too much here. It is actually saying only:
1. Write SEED to each register (five in total).
2. Confirm that STATUS register says seeding done.
3. Start RNG engine.
4. Wait for engine finish (another bit in STATUS - clear it then).
5. Read the randoms.

I would guess that the hardware will ignore all previously written seeds and use the last one. Maybe the hardware will use all of the seeds written as you imply. It is just a guessing.

Oh my, if you are right with your first guess, this is a bad DRNG design.

Just out of curiousity: what happens if a caller invokes the seed function twice or more times (each time with the sufficient amount of bits)? What is your guess here?

Quoted 6 lines

Oh my, if you are right with your first guess, this is a bad DRNG design.

Just out of curiousity: what happens if a caller invokes the seed function twice or more times (each time with the sufficient amount of bits)? What is
your guess here?

Should the second seed use the random data generated by the device?

Am Montag, 27. M?rz 2017, 06:23:11 CEST schrieb PrasannaKumar Muralidharan:

Hi PrasannaKumar,

Quoted 7 lines

Quoted 6 lines

Oh my, if you are right with your first guess, this is a bad DRNG design.

Just out of curiousity: what happens if a caller invokes the seed function twice or more times (each time with the sufficient amount of bits)? What is
your guess here?

Quoted 1 line

Should the second seed use the random data generated by the device?

A DRNG should be capable of processing an arbitrary amount of seed data. It may be the case that the seed data must be processed in chunks though.

That said, it may be the case that after injecting one chunk of seed the currently discussed RNG simply needs to generate a random number to process the input data before another seed can be added. But that is pure speculation.

But I guess that can be easily tested: inject a known seed into the DRNG, generate a random number, inject the same seed again and again generate a random number. If both are identical (which I do not hope), then the internal state is simply overwritten (strange DRNG design).

A similar test can be made to see whether a larger set of seed simply overwrites the state or is really processed.

1. seed
2. generate random data
3. reset
4. seed with anther seed
5. generate random data
6. reset
7. seed with same data from 1
8. seed with same data from 2
9. generate random data

If data from 9 is identical to 2, then additional seed data is discarded -> bad design. If data from 9 is identical to 5, then the additional data overwrites the initial data -> bad DRNG design. If data from 9 neither matches 2 or 5, then all seed is taken -> good design.

I tested a little bit and:
1. Seeding with some value
2. generating random,
3. kcapi_rng_destroy+kcrng_init, (I cannot do a hardware reset except reboot of entire system)
4. seeding with the same value as in (1) - different random numbers.

Doing a system reboot and repeating above - different random numbers (all are different: step (2) and in (4)).

Your test case also produces different random values every time.

Best regards,
Krzysztof

Am Dienstag, 28. M?rz 2017, 18:48:24 CEST schrieb Krzysztof Kozlowski:

Hi Krzysztof,

Quoted 7 lines

I tested a little bit and:
1. Seeding with some value
2. generating random,
3. kcapi_rng_destroy+kcrng_init, (I cannot do a hardware reset except reboot of entire system)
4. seeding with the same value as in (1) - different random numbers.

Quoted 4 lines

Doing a system reboot and repeating above - different random numbers (all are different: step (2) and in (4)).

Your test case also produces different random values every time.

Then I would assume that simply adding an outer loop to your for() loop to inject seed larger than the minimum required seed size should be fine.

Hi,

This is a follow up of my questions around exynos-rng [1].

Changes since v2:
=================
1. Do not re-use random numbers for re-seed (neither for system resume nor for periodic re-seed). Instead the driver will just generate new random numbers (suggested by Stephan M?ller).