i2c: imx: implement bus recovery

Implement bus recovery methods for i2c-imx so we can recover from
situations where SCL/SDA are stuck low.

Once i2c bus SCL/SDA are stuck low during transfer, config the i2c
pinctrl to gpio mode by calling pinctrl sleep set function, and then
use GPIO to emulate the i2c protocol to send nine dummy clock to recover
i2c device. After recovery, set i2c pinctrl to default group setting.

Signed-off-by: Fugang Duan <[e-mail]>
Signed-off-by: Gao Pan <[e-mail]>
Signed-off-by: Sascha Hauer <[e-mail]>
Signed-off-by: Wolfram Sang <[e-mail]>

Documentation/devicetree/bindings/i2c/i2c-imx.txt

···
   The absence of the propoerty indicates the default frequency 100 kHz.
 - dmas: A list of two dma specifiers, one for each entry in dma-names.
 - dma-names: should contain "tx" and "rx".
+- scl-gpios: specify the gpio related to SCL pin
+- sda-gpios: specify the gpio related to SDA pin
+- pinctrl: add extra pinctrl to configure i2c pins to gpio function for i2c
+  bus recovery, call it "gpio" state
 
 Examples:
 
···
 	dmas = <&edma0 0 50>,
 		<&edma0 0 51>;
 	dma-names = "rx","tx";
+	pinctrl-names = "default", "gpio";
+	pinctrl-0 = <&pinctrl_i2c1>;
+	pinctrl-1 = <&pinctrl_i2c1_gpio>;
+	scl-gpios = <&gpio5 26 GPIO_ACTIVE_HIGH>;
+	sda-gpios = <&gpio5 27 GPIO_ACTIVE_HIGH>;
 };

drivers/i2c/busses/i2c-imx.c

···
 #include <linux/of.h>
 #include <linux/of_device.h>
 #include <linux/of_dma.h>
+#include <linux/of_gpio.h>
 #include <linux/platform_data/i2c-imx.h>
 #include <linux/platform_device.h>
 #include <linux/sched.h>
···
 	unsigned int		cur_clk;
 	unsigned int		bitrate;
 	const struct imx_i2c_hwdata	*hwdata;
+	struct i2c_bus_recovery_info rinfo;
+
+	struct pinctrl *pinctrl;
+	struct pinctrl_state *pinctrl_pins_default;
+	struct pinctrl_state *pinctrl_pins_gpio;
 
 	struct imx_i2c_dma	*dma;
 };
···
 
 	/* Start I2C transfer */
 	result = i2c_imx_start(i2c_imx);
+	if (result) {
+		if (i2c_imx->adapter.bus_recovery_info) {
+			i2c_recover_bus(&i2c_imx->adapter);
+			result = i2c_imx_start(i2c_imx);
+		}
+	}
+
 	if (result)
 		goto fail0;
 
···
 		(result < 0) ? "error" : "success msg",
 			(result < 0) ? result : num);
 	return (result < 0) ? result : num;
+}
+
+static void i2c_imx_prepare_recovery(struct i2c_adapter *adap)
+{
+	struct imx_i2c_struct *i2c_imx;
+
+	i2c_imx = container_of(adap, struct imx_i2c_struct, adapter);
+
+	pinctrl_select_state(i2c_imx->pinctrl, i2c_imx->pinctrl_pins_gpio);
+}
+
+static void i2c_imx_unprepare_recovery(struct i2c_adapter *adap)
+{
+	struct imx_i2c_struct *i2c_imx;
+
+	i2c_imx = container_of(adap, struct imx_i2c_struct, adapter);
+
+	pinctrl_select_state(i2c_imx->pinctrl, i2c_imx->pinctrl_pins_default);
+}
+
+static void i2c_imx_init_recovery_info(struct imx_i2c_struct *i2c_imx,
+		struct platform_device *pdev)
+{
+	struct i2c_bus_recovery_info *rinfo = &i2c_imx->rinfo;
+
+	i2c_imx->pinctrl_pins_default = pinctrl_lookup_state(i2c_imx->pinctrl,
+			PINCTRL_STATE_DEFAULT);
+	i2c_imx->pinctrl_pins_gpio = pinctrl_lookup_state(i2c_imx->pinctrl,
+			"gpio");
+	rinfo->sda_gpio = of_get_named_gpio_flags(pdev->dev.of_node,
+			"sda-gpios", 0, NULL);
+	rinfo->scl_gpio = of_get_named_gpio_flags(pdev->dev.of_node,
+			"scl-gpios", 0, NULL);
+
+	if (!gpio_is_valid(rinfo->sda_gpio) ||
+	    !gpio_is_valid(rinfo->scl_gpio) ||
+	    IS_ERR(i2c_imx->pinctrl_pins_default) ||
+	    IS_ERR(i2c_imx->pinctrl_pins_gpio)) {
+		dev_dbg(&pdev->dev, "recovery information incomplete\n");
+		return;
+	}
+
+	dev_dbg(&pdev->dev, "using scl-gpio %d and sda-gpio %d for recovery\n",
+			rinfo->sda_gpio, rinfo->scl_gpio);
+
+	rinfo->prepare_recovery = i2c_imx_prepare_recovery;
+	rinfo->unprepare_recovery = i2c_imx_unprepare_recovery;
+	rinfo->recover_bus = i2c_generic_gpio_recovery;
+	i2c_imx->adapter.bus_recovery_info = rinfo;
 }
 
 static u32 i2c_imx_func(struct i2c_adapter *adapter)
···
 		dev_err(&pdev->dev, "can't enable I2C clock\n");
 		return ret;
 	}
+
+	i2c_imx->pinctrl = devm_pinctrl_get(&pdev->dev);
+	if (IS_ERR(i2c_imx->pinctrl)) {
+		ret = PTR_ERR(i2c_imx->pinctrl);
+		goto clk_disable;
+	}
+
 	/* Request IRQ */
 	ret = devm_request_irq(&pdev->dev, irq, i2c_imx_isr, 0,
 				pdev->name, i2c_imx);
···
 		dev_err(&pdev->dev, "registration failed\n");
 		goto clk_disable;
 	}
+
+	i2c_imx_init_recovery_info(i2c_imx, pdev);
 
 	/* Set up platform driver data */
 	platform_set_drvdata(pdev, i2c_imx);