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From:   shubhrajyoti.datta@gmail.com
To:     linux-kernel@vger.kernel.org, linux-i2c@vger.kernel.org
Cc:     michal.simek@xilinx.com, Chirag Parekh <chiragp@xilinx.com>,
        Nava kishore Manne <navam@xilinx.com>,
        Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Subject: [PATCH 4/4] i2c: cadence: Recover bus after controller reset
Date:   Mon,  9 Dec 2019 16:10:52 +0530
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From: Chirag Parekh <chiragp@xilinx.com>

This will save from potential lock-up caused when I2c master controller
resets in the middle of transfer and the slave is holding SDA line to
transmit more data.

Signed-off-by: Chirag Parekh <chiragp@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Nava kishore Manne <navam@xilinx.com>
Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
---
 drivers/i2c/busses/i2c-cadence.c | 101 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 101 insertions(+)

diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
index 8a2983e..e11e986 100644
--- a/drivers/i2c/busses/i2c-cadence.c
+++ b/drivers/i2c/busses/i2c-cadence.c
@@ -7,13 +7,16 @@
 
 #include <linux/clk.h>
 #include <linux/delay.h>
+#include <linux/gpio/consumer.h>
 #include <linux/i2c.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/of.h>
+#include <linux/of_gpio.h>
 #include <linux/pm_runtime.h>
+#include <linux/pinctrl/consumer.h>
 
 /* Register offsets for the I2C device. */
 #define CDNS_I2C_CR_OFFSET		0x00 /* Control Register, RW */
@@ -139,6 +142,10 @@
  * @clk_rate_change_nb:	Notifier block for clock rate changes
  * @quirks:		flag for broken hold bit usage in r1p10
  * @ctrl_reg:		Cached value of the control register.
+ * @rinfo:		Structure holding recovery information.
+ * @pinctrl:		Pin control state holder.
+ * @pinctrl_pins_default: Default pin control state.
+ * @pinctrl_pins_gpio:	GPIO pin control state.
  */
 struct cdns_i2c {
 	struct device		*dev;
@@ -160,6 +167,10 @@ struct cdns_i2c {
 	struct notifier_block clk_rate_change_nb;
 	u32 quirks;
 	u32 ctrl_reg;
+	struct i2c_bus_recovery_info rinfo;
+	struct pinctrl *pinctrl;
+	struct pinctrl_state *pinctrl_pins_default;
+	struct pinctrl_state *pinctrl_pins_gpio;
 };
 
 struct cdns_platform_data {
@@ -544,6 +555,7 @@ static int cdns_i2c_process_msg(struct cdns_i2c *id, struct i2c_msg *msg,
 	/* Wait for the signal of completion */
 	time_left = wait_for_completion_timeout(&id->xfer_done, adap->timeout);
 	if (time_left == 0) {
+		i2c_recover_bus(adap);
 		cdns_i2c_master_reset(adap);
 		dev_err(id->adap.dev.parent,
 				"timeout waiting on completion\n");
@@ -880,6 +892,88 @@ static int __maybe_unused cdns_i2c_runtime_resume(struct device *dev)
 	return 0;
 }
 
+/**
+ * cdns_i2c_prepare_recovery - Withhold recovery state
+ * @adapter:    Pointer to i2c adapter
+ *
+ * This function is called to prepare for recovery.
+ * It changes the state of pins from SCL/SDA to GPIO.
+ */
+static void cdns_i2c_prepare_recovery(struct i2c_adapter *adapter)
+{
+	struct cdns_i2c *p_cdns_i2c;
+
+	p_cdns_i2c = container_of(adapter, struct cdns_i2c, adap);
+
+	/* Setting pin state as gpio */
+	pinctrl_select_state(p_cdns_i2c->pinctrl,
+			p_cdns_i2c->pinctrl_pins_gpio);
+}
+
+/**
+ * cdns_i2c_unprepare_recovery - Release recovery state
+ * @adapter:    Pointer to i2c adapter
+ *
+ * This function is called on exiting recovery. It reverts
+ * the state of pins from GPIO to SCL/SDA.
+ */
+static void cdns_i2c_unprepare_recovery(struct i2c_adapter *adapter)
+{
+	struct cdns_i2c *p_cdns_i2c;
+
+	p_cdns_i2c = container_of(adapter, struct cdns_i2c, adap);
+
+	/* Setting pin state to default(i2c) */
+	pinctrl_select_state(p_cdns_i2c->pinctrl,
+			p_cdns_i2c->pinctrl_pins_default);
+}
+
+/**
+ * cdns_i2c_init_recovery_info  - Initialize I2C bus recovery
+ * @pid:        Pointer to cdns i2c structure
+ * @pdev:       Handle to the platform device structure
+ *
+ * This function does required initialization for i2c bus
+ * recovery. It registers three functions for prepare,
+ * recover and unprepare
+ *
+ * Return: 0 on Success, negative error otherwise.
+ */
+static int cdns_i2c_init_recovery_info(struct cdns_i2c *pid,
+		struct platform_device *pdev)
+{
+	struct i2c_bus_recovery_info *rinfo = &pid->rinfo;
+
+	pid->pinctrl_pins_default = pinctrl_lookup_state(pid->pinctrl,
+			PINCTRL_STATE_DEFAULT);
+	pid->pinctrl_pins_gpio = pinctrl_lookup_state(pid->pinctrl, "gpio");
+
+	/* Fetches GPIO pins */
+	rinfo->sda_gpiod = devm_gpiod_get(&pdev->dev, "sda-gpios", 0);
+	rinfo->scl_gpiod = devm_gpiod_get(&pdev->dev, "scl-gpios", 0);
+
+	/* if GPIO driver isn't ready yet, deffer probe */
+	if (PTR_ERR(rinfo->sda_gpiod) == -EPROBE_DEFER ||
+	    PTR_ERR(rinfo->scl_gpiod) == -EPROBE_DEFER)
+		return -EPROBE_DEFER;
+
+	/* Validates fetched information */
+	if (IS_ERR(rinfo->sda_gpiod) ||
+	    IS_ERR(rinfo->scl_gpiod) ||
+			IS_ERR(pid->pinctrl_pins_default) ||
+			IS_ERR(pid->pinctrl_pins_gpio)) {
+		dev_dbg(&pdev->dev, "recovery information incomplete\n");
+		return 0;
+	}
+
+	rinfo->prepare_recovery     = cdns_i2c_prepare_recovery;
+	rinfo->unprepare_recovery   = cdns_i2c_unprepare_recovery;
+	rinfo->recover_bus          = i2c_generic_scl_recovery;
+	pid->adap.bus_recovery_info = rinfo;
+
+	return 0;
+}
+
 static const struct dev_pm_ops cdns_i2c_dev_pm_ops = {
 	SET_RUNTIME_PM_OPS(cdns_i2c_runtime_suspend,
 			   cdns_i2c_runtime_resume, NULL)
@@ -926,6 +1020,13 @@ static int cdns_i2c_probe(struct platform_device *pdev)
 		id->quirks = data->quirks;
 	}
 
+	id->pinctrl = devm_pinctrl_get(&pdev->dev);
+	if (!IS_ERR(id->pinctrl)) {
+		ret = cdns_i2c_init_recovery_info(id, pdev);
+		if (ret)
+			return ret;
+	}
+
 	r_mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	id->membase = devm_ioremap_resource(&pdev->dev, r_mem);
 	if (IS_ERR(id->membase))
-- 
2.1.1