Introduce caching support for regmap

This patch introduces caching support for regmap. The regcache API has evolved essentially out of ASoC soc-cache so most of the actual caching types (except LZO) have been tested in the past.

The purpose of regcache is to optimize in time and space the handling of register caches. Time optimization is achieved by not having to go over a slow bus like I2C to read the value of a register, instead it is cached locally in memory and can be retrieved faster. Regarding space optimization, some of the cache types are better at packing the caches, for e.g. the rbtree and the LZO caches. By doing this the sacrifice in time still wins over doing I2C transactions.

Signed-off-by Dimitris Papastamos <[email protected]>

---
 drivers/base/regmap/Makefile   |    2 +-
 drivers/base/regmap/internal.h |   52 +++++++
 drivers/base/regmap/regcache.c |  302 ++++++++++++++++++++++++++++++++++++++++
 include/linux/regmap.h         |   24 +++-
 4 files changed, 374 insertions(+), 6 deletions(-)
 create mode 100644 drivers/base/regmap/regcache.c

drivers/base/regmap/Makefile +1 -1

index 057c13f..2e103ea 100644
@@ -1,4 +1,4 @@
-obj-$(CONFIG_REGMAP) += regmap.o
+obj-$(CONFIG_REGMAP) += regmap.o regcache.o
 obj-$(CONFIG_DEBUG_FS) += regmap-debugfs.o
 obj-$(CONFIG_REGMAP_I2C) += regmap-i2c.o
 obj-$(CONFIG_REGMAP_SPI) += regmap-spi.o

drivers/base/regmap/internal.h +52 -0

index 5ab3fef..dbeccd2 100644
@@ -17,6 +17,7 @@
 #include <linux/fs.h>
 
 struct regmap;
+struct regcache_ops;
 
 struct regmap_format {
 	size_t buf_size;

@@ -46,6 +47,40 @@ struct regmap {
 	bool (*readable_reg)(struct device *dev, unsigned int reg);
 	bool (*volatile_reg)(struct device *dev, unsigned int reg);
 	bool (*precious_reg)(struct device *dev, unsigned int reg);
+
+	/* regcache specific members */
+	const struct regcache_ops *cache_ops;
+	enum regcache_type cache_type;
+
+	/* number of bytes in cache_defaults_raw */
+	unsigned int cache_size_raw;
+	/* number of bytes per word in cache_defaults_raw */
+	unsigned int cache_word_size;
+	/* number of entries in cache_defaults */
+	unsigned int num_cache_defaults;
+	/* number of entries in cache_defaults_raw */
+	unsigned int num_cache_defaults_raw;
+
+	/* if set, only the cache is modified not the HW */
+	unsigned int cache_only:1;
+	/* if set, only the HW is modified not the cache */
+	unsigned int cache_bypass:1;
+	/* if set, remember to free cache_defaults_raw */
+	unsigned int cache_free:1;
+
+	struct reg_default *cache_defaults;
+	const void *cache_defaults_raw;
+	void *cache;
+};
+
+struct regcache_ops {
+	const char *name;
+	enum regcache_type type;
+	int (*init)(struct regmap *map);
+	int (*exit)(struct regmap *map);
+	int (*read)(struct regmap *map, unsigned int reg, unsigned int *value);
+	int (*write)(struct regmap *map, unsigned int reg, unsigned int value);
+	int (*sync)(struct regmap *map);
 };
 
 bool regmap_writeable(struct regmap *map, unsigned int reg);

@@ -63,4 +98,21 @@ void regmap_debugfs_init(struct regmap *map) { }
 void regmap_debugfs_exit(struct regmap *map) { }
 #endif
 
+/* regcache core declarations */
+int regcache_init(struct regmap *map);
+void regcache_exit(struct regmap *map);
+int regcache_read(struct regmap *map,
+		       unsigned int reg, unsigned int *value);
+int regcache_write(struct regmap *map,
+			unsigned int reg, unsigned int value);
+int regcache_sync(struct regmap *map);
+
+unsigned int regcache_get_val(const void *base, unsigned int idx,
+			      unsigned int word_size);
+bool regcache_set_val(void *base, unsigned int idx,
+		      unsigned int val, unsigned int word_size);
+int regcache_lookup_reg(struct regmap *map, unsigned int reg);
+int regcache_insert_reg(struct regmap *map, unsigned int reg,
+			unsigned int val);
+
 #endif

drivers/base/regmap/regcache.c new file +53 -0

new file mode 100644
index 0000000..f26df00
@@ -0,0 +1,302 @@
+/*
+ * Register cache access API
+ *
+ * Copyright 2011 Wolfson Microelectronics plc
+ *
+ * Author: Dimitris Papastamos <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/slab.h>
+#include <trace/events/regmap.h>
+
+#include "internal.h"
+
+static const struct regcache_ops *cache_types[] = {
+};
+
+int regcache_init(struct regmap *map)
+{
+	int i, j;
+	int count;
+	int ret;
+	unsigned int val;
+	void *tmp_buf;
+
+	if (map->cache_type == REGCACHE_NONE)
+		return 0;
+
+	for (i = 0; i < ARRAY_SIZE(cache_types); i++)
+		if (cache_types[i]->type == map->cache_type)
+			break;
+
+	if (i == ARRAY_SIZE(cache_types)) {
+		dev_err(map->dev, "Could not match compress type: %d\n",
+			map->cache_type);
+		return -EINVAL;
+	}
+
+	map->cache = NULL;
+	map->cache_ops = cache_types[i];
+
+	if (!map->cache_ops->read ||
+	    !map->cache_ops->write ||
+	    !map->cache_ops->name)
+		return -EINVAL;
+
+	/* We still need to ensure that the cache_defaults
+	 * won't vanish from under us.  We'll need to make
+	 * a copy of it.
+	 */

drivers/base/regmap/regcache.c new file +68 -0

+	/* Some devices such as PMIC's don't have cache defaults,
+	 * we cope with this by reading back the HW registers and
+	 * crafting the cache defaults by hand.
+	 */
+	if (!map->cache_defaults_raw) {
+		if (!map->num_cache_defaults_raw)
+			return -EINVAL;
+		dev_warn(map->dev, "No cache defaults, reading back from HW\n");
+		tmp_buf = kmalloc(map->cache_size_raw, GFP_KERNEL);
+		if (!tmp_buf)
+			return -EINVAL;
+		ret = regmap_bulk_read(map, 0, tmp_buf,
+				       map->num_cache_defaults_raw);
+		if (ret < 0) {
+			kfree(tmp_buf);
+			return ret;
+		}
+		map->cache_defaults_raw = tmp_buf;
+		map->cache_free = 1;
+	}
+
+	/* calculate the size of cache_defaults */
+	for (count = 0, i = 0; i < map->num_cache_defaults_raw; i++) {
+		val = regcache_get_val(map->cache_defaults_raw,
+				       i, map->cache_word_size);
+		if (!val)
+			continue;
+		count++;
+	}
+
+	map->cache_defaults = kmalloc(count * sizeof(struct reg_default),
+				      GFP_KERNEL);
+	if (!map->cache_defaults)
+		return -ENOMEM;
+
+	/* fill the cache_defaults */
+	map->num_cache_defaults = count;
+	for (i = 0, j = 0; i < map->num_cache_defaults_raw; i++) {
+		val = regcache_get_val(map->cache_defaults_raw,
+				       i, map->cache_word_size);
+		if (!val)
+			continue;
+		map->cache_defaults[j].reg = i;
+		map->cache_defaults[j].def = val;
+		j++;
+	}
+
+cache_init:
+	if (map->cache_ops->init) {
+		dev_dbg(map->dev, "Initializing %s cache\n",
+			map->cache_ops->name);
+		return map->cache_ops->init(map);
+	}
+	return 0;
+}
+
[...]
+
+/**
+ * regcache_read: Fetch the value of a given register from the cache.
+ *
+ * @map: map to configure.
+ * @reg: The register index.
+ * @value: The value to be returned.
+ *
+ * Return a negative value on failure, 0 on success.
+ */
+int regcache_read(struct regmap *map,
+		  unsigned int reg, unsigned int *value)

drivers/base/regmap/regcache.c new file +24 -0

+
+	if (map->max_register)
+		max_reg = map->max_register;
+	else
+		max_reg = map->num_cache_defaults_raw;
+
+
+	if (reg < max_reg && !regmap_volatile(map, reg))
+		return map->cache_ops->read(map, reg, value);
+	return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(regcache_read);
+
+/**
+ * regcache_write: Set the value of a given register in the cache.
+ *
+ * @map: map to configure.
+ * @reg: The register index.
+ * @value: The new register value.
+ *
+ * Return a negative value on failure, 0 on success.
+ */
+int regcache_write(struct regmap *map,
+		   unsigned int reg, unsigned int value)

drivers/base/regmap/regcache.c new file +12 -0

+
+	if (map->max_register)
+		max_reg = map->max_register;
+	else
+		max_reg = map->num_cache_defaults_raw;
+
+	if (reg < max_reg && !regmap_volatile(map, reg))
+		return map->cache_ops->write(map, reg, value);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(regcache_write);
+
[...]

include/linux/regmap.h +13 -3

index 449e264..7591e01 100644
@@ -20,6 +20,11 @@
 struct i2c_client;
 struct spi_device;
 
+/* An enum of all the supported cache types */
+enum regcache_type {
+	REGCACHE_NONE,
+};
+
 /**
  * Default value for a register.  We use an array of structs rather
  * than a simple array as many modern devices have very sparse

@@ -50,9 +55,14 @@ struct reg_default {
  *                (eg, a clear on read interrupt status register).
  *
  * @max_register: Optional, specifies the maximum valid register index.
- * @reg_defaults: Power on reset values for registers (for use with
- *                register cache support).
- * @num_reg_defaults: Number of elements in reg_defaults.
+ *
+ * @cache_type: The actual cache type.
+ * @cache_defaults: Power on reset values for registers (for use with
+ *                  register cache support).
+ * @num_cache_defaults: Number of elements in cache_defaults.
+ * @cache_defaults_raw: Power on reset values for registers (for use with
+ *                 register cache support).
+ * @num_cache_defaults_raw: Number of elements in cache_defaults_raw.
  */
 struct regmap_config {
 	int reg_bits;

include/linux/regmap.h +3 -0

+	unsigned int num_cache_defaults;
+	const void *cache_defaults_raw;
+	unsigned int num_cache_defaults_raw;
 };

[...]

drivers/base/regmap/regcache-rbtree.c new file +9 -0

+
+static int regcache_rbtree_init(struct regmap *map)
+{
+	struct regcache_rbtree_ctx *rbtree_ctx;
+	int i;
+	int ret;
+
+	map->cache = kmalloc(sizeof *rbtree_ctx, GFP_KERNEL);
+	if (!map->cache)

drivers/base/regmap/regcache-rbtree.c new file +10 -0

+		if (ret)
+			goto err;
+	}
+
+	return 0;
+
+err:
+	regcache_exit(map);
+	return ret;
+}
[...]

This patch adds support for LZO compression when storing the register cache.

For a typical device whose register map would normally occupy 25kB or 50kB by using the LZO compression technique, one can get down to ~5-7kB. There might be a performance penalty associated with each individual read/write due to decompressing/compressing the underlying cache, however that should not be noticeable. These memory benefits depend on whether the target architecture can get rid of the memory occupied by the original register defaults cache which is marked as __devinitconst. Nevertheless there will be some memory gain even if the target architecture can't get rid of the original register map, this should be around ~30-32kB instead of 50kB.

Signed-off-by Dimitris Papastamos <[email protected]>

---
 drivers/base/regmap/Makefile       |    2 +-
 drivers/base/regmap/internal.h     |    2 +
 drivers/base/regmap/regcache-lzo.c |  361 ++++++++++++++++++++++++++++++++++++
 drivers/base/regmap/regcache.c     |    1 +
 include/linux/regmap.h             |    1 +
 5 files changed, 366 insertions(+), 1 deletions(-)
 create mode 100644 drivers/base/regmap/regcache-lzo.c

Quoted 14 lines · Dimitris Papastamos

This patch adds support for LZO compression when storing the register cache.

For a typical device whose register map would normally occupy 25kB or 50kB by using the LZO compression technique, one can get down to ~5-7kB. There might be a performance penalty associated with each individual read/write due to decompressing/compressing the underlying cache, however that should not be noticeable. These memory benefits depend on whether the target architecture can get rid of the memory occupied by the original register defaults cache which is marked as __devinitconst. Nevertheless there will be some memory gain even if the target architecture can't get rid of the original register map, this should be around ~30-32kB instead of 50kB.

Signed-off-by Dimitris Papastamos <[email protected]>

Quoted 9 lines

---
 drivers/base/regmap/Makefile       |    2 +-
 drivers/base/regmap/internal.h     |    2 +
 drivers/base/regmap/regcache-lzo.c |  361 ++++++++++++++++++++++++++++++++++++
 drivers/base/regmap/regcache.c     |    1 +
 include/linux/regmap.h             |    1 +
 5 files changed, 366 insertions(+), 1 deletions(-)
 create mode 100644 drivers/base/regmap/regcache-lzo.c

Fails to compile due to CONFIG_LZO_{COMPRESS,DECOMPRESS} not being selected. Also it will have issues, with caches where we don't use raw cache defaults.

This patch incorporates the regcache core code into regmap. All previous patches have been no-ops essentially up to this point.

The bulk read operation is not supported by regcache at the moment. This will be implemented incrementally.

Signed-off-by Dimitris Papastamos <[email protected]>

---
 drivers/base/regmap/regmap.c |   56 ++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 56 insertions(+), 0 deletions(-)

drivers/base/regmap/regmap.c +7 -0

index fa2bd89..df4e00a 100644
@@ -146,6 +146,13 @@ struct regmap *regmap_init(struct device *dev,
 	map->readable_reg = config->readable_reg;
 	map->volatile_reg = config->volatile_reg;
 	map->precious_reg = config->precious_reg;
+	map->cache_type = config->cache_type;
+	map->cache_defaults = config->cache_defaults;
+	map->num_cache_defaults = config->num_cache_defaults;
+	map->num_cache_defaults_raw = config->num_cache_defaults_raw;
+	map->cache_defaults_raw = config->cache_defaults_raw;
+	map->cache_size_raw = (config->val_bits / 8) * config->num_cache_defaults_raw;
+	map->cache_word_size = config->val_bits / 8;
 
 	switch (config->reg_bits) {
 	case 4:

drivers/base/regmap/regmap.c +22 -0

+	ret = regcache_init(map);
+	if (ret < 0)
+		goto err_bus;
+#endif
+
 	regmap_debugfs_init(map);
 
 	return map;

@@ -219,6 +232,9 @@ EXPORT_SYMBOL_GPL(regmap_init);
  */
 void regmap_exit(struct regmap *map)
 {
+#ifdef CONFIG_REGCACHE
+	regcache_exit(map);
+#endif
 	regmap_debugfs_exit(map);
 	kfree(map->work_buf);
 	module_put(map->bus->owner);

@@ -321,6 +337,20 @@ int regmap_write(struct regmap *map, unsigned int reg, unsigned int val)
 
 	mutex_lock(&map->lock);
 
+#ifdef CONFIG_REGCACHE
+	if (!map->cache_bypass) {
+		ret = regcache_write(map, reg, val);
+		if (ret < 0) {
+			mutex_unlock(&map->lock);
+			return ret;
+		}
+		if (map->cache_only) {
+			mutex_unlock(&map->lock);
+			return 0;
+		}
+	}
+#endif
+
 	ret = _regmap_write(map, reg, val);
 
 	mutex_unlock(&map->lock);

@@ -422,6 +452,16 @@ int regmap_read(struct regmap *map, unsigned int reg, unsigned int *val)
 

drivers/base/regmap/regmap.c +2 -0

+#endif
+
 	ret = _regmap_read(map, reg, val);
 
 	mutex_unlock(&map->lock);

drivers/base/regmap/regmap.c int regmap_read(struct regmap *map, unsigned int reg, unsigned int *val) · line 462

Quoted 8 lines · Dimitris Papastamos

drivers/base/regmap/regmap.c +8 -0

+#ifdef CONFIG_REGCACHE
+	if (!map->cache_bypass) {
+		ret = regcache_read(map, reg, val);
+		if (!ret) {
+			mutex_unlock(&map->lock);
+			return 0;
+		}
+	}

I think this will need tighter integration. For example do we want to fallback to a hw read when the cached read fails? And also regcache_read will return for REGCACHE_NONE, which means we neither do a cached read nor a hw read.

This patch series introduces register caching support for regmap. I've implemented all the suggestions since v1, except the use of a dedicated init function for each of the compress types. Due to lack of time, I'll submit the updated patches in a couple of days. I'm aware this can't be merged as is due to this outstanding change, but I'm posting it in any case for reviewing.