Extend dt bindings to support I2C on sifive devices and a fix broken IRQ in polling mode.

The patch is based on mainline v5.2-rc1 and extends DT-bindings for Opencore based I2C IP block reimplemented in FU540 SoC, available on HiFive unleashed board (Rev A00), and also provides a workaround for broken IRQ which affects the already available I2C polling mode interface in mainline, for FU540-C000 chipsets.

The polling mode workaround patch fixes the CPU stall issue, when-ever i2c transfer are initiated.

This workaround checks if it's a FU540 chipset based on device tree information, and check's for open core's IF(interrupt flag) and BUSY flags to break from the polling loop upon completion of transfer.

To test the patch, a PMOD-AD2 sensor is connected to HiFive Unleashed board over J1 connector, and appropriate device node is added into board specific device tree as per the information provided in dt-bindings in Documentation/devicetree/bindings/i2c/i2c-ocores.txt.
Without this workaround, the CPU stall's infinitely.

Busybox i2c utilities used to verify workaround : i2cdetect, i2cdump, i2cset, i2cget

Patch History:
V7<->V8:
-Incorporated review comments for cosmetic changes like: space, comma and period(.)

V6<->V7:
-Rectified space and tab issue in dt bindings strings. -Implemented workaround based on i2c->flags, as per review comment on v6.

V5<->V6:
-Incorporated suggestions on v5 patch as follows:
-Reformatted compatibility strings in dt doc with one valid combination on each line.
-Removed interrupt-parents from optional property list.
-With rebase to v5.2-rc1, the v5 variant of polling workaround PATCH becomes in-compatible.
Till kernel v5.1 the polling mode was enabled based on i2c->flags, wherease in kernel v5.2-rc1 polling mode is set as master transfer algorithim at probe time itself, and i2c->flags checks are removed.
-Modified v5 to check for SiFive device type in polling function and include the workaround/fix for broken IRQ.

v4<->V5:
-Removed un-necessary checks of OCORES_FLAG_BROKEN_IRQ.

V3<->V4:
-Incorporated suggestions on v3 patch as follows:
-OCORES_FLAG_BROKEN_IRQ BIT position rectified.
-Updated BORKEN_IRQ flag checks such that if sifive device (Fu540-C000) is identified,then use polling mode as IRQ is broken.

V2<->V3:
-Incorporated review comments on v2 patch as follows:
-Rectified compatibility string sequence with the most specific one at the first (dt bindings). -Moved interrupts and interrupt-parent under optional property list (dt-bindings). -Updated reference to sifive-blocks-ip-versioning.txt and URL to IP repository used (dt-bindings). -Removed example for i2c0 device node from binding doc (dt-bindings).
-Included sifive,i2c0 device under compatibility table in i2c-ocores driver (i2c-ocores). -Updated polling mode hooks for SoC specific fix to handle broken IRQ (i2c-ocores).

V1<->V2:
-Incorporate review comments from Andrew
-Extend dt bindings into i2c-ocores.txt instead of adding new file -Rename SIFIVE_FLAG_POLL to OCORES_FLAG_BROKEN_IRQ

V1:
-Update dt bindings for sifive i2c devices -Fix broken IRQ affecting i2c polling mode interface.

Sagar Shrikant Kadam (3):
dt-bindings: i2c: extend existing opencore bindings.
i2c-ocores: sifive: add support for i2c device on FU540-c000 SoC.
i2c-ocores: sifive: add polling mode workaround for FU540-C000 SoC.

 .../devicetree/bindings/i2c/i2c-ocores.txt         |  9 ++++--
 drivers/i2c/busses/i2c-ocores.c                    | 33 ++++++++++++++++++++--
 2 files changed, 38 insertions(+), 4 deletions(-)

1.9.1

Reformatted compatibility strings to one valid combination on each line.
Add FU540-C000 specific device tree bindings to already available i2-ocores file. This device is available on
HiFive Unleashed Rev A00 board. Move interrupt under optional property list as this can be optional.

The FU540-C000 SoC from sifive, has an Opencore's I2C block reimplementation.

The DT compatibility string for this IP is present in HDL and available at.
https://github.com/sifive/sifive-blocks/blob/master/src/main/scala/devices/i2c/I2C.scala#L73

---
 Documentation/devicetree/bindings/i2c/i2c-ocores.txt | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

index 17bef9a..6b25a80 100644
@@ -1,9 +1,13 @@
 Device tree configuration for i2c-ocores
 
 Required properties:
-- compatible      : "opencores,i2c-ocores" or "aeroflexgaisler,i2cmst"
+- compatible      : "opencores,i2c-ocores"
+                    "aeroflexgaisler,i2cmst"
+                    "sifive,fu540-c000-i2c", "sifive,i2c0"
+                    For Opencore based I2C IP block reimplemented in
+                    FU540-C000 SoC. Please refer to sifive-blocks-ip-versioning.txt
+                    for additional details.
 - reg             : bus address start and address range size of device
-- interrupts      : interrupt number
 - clocks          : handle to the controller clock; see the note below.
                     Mutually exclusive with opencores,ip-clock-frequency
 - opencores,ip-clock-frequency: frequency of the controller clock in Hz;

@@ -12,6 +16,7 @@ Required properties:
 - #size-cells     : should be <0>
 
 Optional properties:
+- interrupts      : interrupt number.
 - clock-frequency : frequency of bus clock in Hz; see the note below.
                     Defaults to 100 KHz when the property is not specified
 - reg-shift       : device register offsets are shifted by this value

1.9.1

Applied to for-next, thanks!

Update device id table for Opencore's I2C master based re-implementation used in FU540-c000 chipset on HiFive Unleashed platform.

Device ID's include Sifive, soc-specific device for chip specific tweaks and sifive IP block specific device for generic programming model.

---
 drivers/i2c/busses/i2c-ocores.c | 9 +++++++++
 1 file changed, 9 insertions(+)

index c3dabee..b334fa2 100644
@@ -82,6 +82,7 @@ struct ocores_i2c {
 
 #define TYPE_OCORES		0
 #define TYPE_GRLIB		1
+#define TYPE_SIFIVE_REV0	2
 
 static void oc_setreg_8(struct ocores_i2c *i2c, int reg, u8 value)
 {

@@ -462,6 +463,14 @@ static u32 ocores_func(struct i2c_adapter *adap)
 		.compatible = "aeroflexgaisler,i2cmst",
 		.data = (void *)TYPE_GRLIB,
 	},
+	{
+		.compatible = "sifive,fu540-c000-i2c",
+		.data = (void *)TYPE_SIFIVE_REV0,
+	},
+	{
+		.compatible = "sifive,i2c0",
+		.data = (void *)TYPE_SIFIVE_REV0,
+	},
 	{},
 };
 MODULE_DEVICE_TABLE(of, ocores_i2c_match);

1.9.1

Applied to for-next, thanks!

The i2c-ocore driver already has a polling mode interface.But it needs a workaround for FU540 Chipset on HiFive unleashed board (RevA00). There is an erratum in FU540 chip that prevents interrupt driven i2c transfers from working, and also the I2C controller's interrupt bit cannot be cleared if set, due to this the existing i2c polling mode interface added in mainline earlier doesn't work, and CPU stall's infinitely, when-ever i2c transfer is initiated.

Ref:
commit dd7dbf0eb090 ("i2c: ocores: refactor setup for polling")

The workaround / fix under OCORES_FLAG_BROKEN_IRQ is particularly for FU540-COOO SoC.

The polling function identifies a SiFive device based on the device node and enables the workaround.

---
 drivers/i2c/busses/i2c-ocores.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

index b334fa2..4117f1a 100644
@@ -35,6 +35,7 @@ struct ocores_i2c {
 	int iobase;
 	u32 reg_shift;
 	u32 reg_io_width;
+	unsigned long flags;
 	wait_queue_head_t wait;
 	struct i2c_adapter adap;
 	struct i2c_msg *msg;

@@ -84,6 +85,8 @@ struct ocores_i2c {
 #define TYPE_GRLIB		1
 #define TYPE_SIFIVE_REV0	2
 
+#define OCORES_FLAG_BROKEN_IRQ BIT(1) /* Broken IRQ for FU540-C000 SoC */
+
 static void oc_setreg_8(struct ocores_i2c *i2c, int reg, u8 value)
 {
 	iowrite8(value, i2c->base + (reg << i2c->reg_shift));

@@ -236,9 +239,12 @@ static irqreturn_t ocores_isr(int irq, void *dev_id)
 	struct ocores_i2c *i2c = dev_id;
 	u8 stat = oc_getreg(i2c, OCI2C_STATUS);
 
-	if (!(stat & OCI2C_STAT_IF))
+	if (i2c->flags & OCORES_FLAG_BROKEN_IRQ) {
+		if ((stat & OCI2C_STAT_IF) && !(stat & OCI2C_STAT_BUSY))
+			return IRQ_NONE;
+	} else if (!(stat & OCI2C_STAT_IF)) {
 		return IRQ_NONE;
-
+	}
 	ocores_process(i2c, stat);
 
 	return IRQ_HANDLED;

@@ -353,6 +359,11 @@ static void ocores_process_polling(struct ocores_i2c *i2c)
 		ret = ocores_isr(-1, i2c);
 		if (ret == IRQ_NONE)
 			break; /* all messages have been transferred */
+		else {
+			if (i2c->flags & OCORES_FLAG_BROKEN_IRQ)
+				if (i2c->state == STATE_DONE)
+					break;
+		}
 	}
 }
 

@@ -595,6 +606,7 @@ static int ocores_i2c_probe(struct platform_device *pdev)
 {
 	struct ocores_i2c *i2c;
 	struct ocores_i2c_platform_data *pdata;
+	const struct of_device_id *match;
 	struct resource *res;
 	int irq;
 	int ret;

@@ -677,6 +689,14 @@ static int ocores_i2c_probe(struct platform_device *pdev)
 	irq = platform_get_irq(pdev, 0);
 	if (irq == -ENXIO) {
 		ocores_algorithm.master_xfer = ocores_xfer_polling;
+
+		/*
+		 * Set in OCORES_FLAG_BROKEN_IRQ to enable workaround for
+		 * FU540-C000 SoC in polling mode.
+		 */
+		match = of_match_node(ocores_i2c_match, pdev->dev.of_node);
+		if (match && (long)match->data == TYPE_SIFIVE_REV0)
+			i2c->flags |= OCORES_FLAG_BROKEN_IRQ;
 	} else {
 		if (irq < 0)
 			return irq;

1.9.1

Applied to for-next, thanks!