[PATCH] i2c-gpio: Add support for deferred probing

[Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>]

GPIOs may not be available immediately when i2c-gpio looks for them.
Implement support for deferred probing so that probing can be
attempted again later when GPIO pins are finally available.

Signed-off-by: Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>
Cc: Haavard Skinnemoen <hskinnemoen-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
A little more changes were needed than I initially thought, because we
want to check the pins before we allocate memory. Otherwise we would
have a possibly large number of memory allocation and freeing cycles
until GPIO pins are finally available.

I wrote this quite some time ago already, but I do not have any system
to test it. I would appreciate if one or more users of the i2c-gpio
driver could give it a try and confirm it works as intended, or at
least doesn't introduce any regression. Thanks.

 drivers/i2c/busses/i2c-gpio.c |   75 ++++++++++++++++++++++++++++--------------
 1 file changed, 50 insertions(+), 25 deletions(-)

--- linux-3.8-rc2.orig/drivers/i2c/busses/i2c-gpio.c	2013-01-09 22:26:30.031060312 +0100
+++ linux-3.8-rc2/drivers/i2c/busses/i2c-gpio.c	2013-01-09 22:32:59.950308645 +0100
@@ -85,23 +85,29 @@ static int i2c_gpio_getscl(void *data)
 	return gpio_get_value(pdata->scl_pin);
 }
 
-static int of_i2c_gpio_probe(struct device_node *np,
-			     struct i2c_gpio_platform_data *pdata)
+static int of_i2c_gpio_get_pins(struct device_node *np,
+				unsigned int *sda_pin, unsigned int *scl_pin)
 {
-	u32 reg;
-
 	if (of_gpio_count(np) < 2)
 		return -ENODEV;
 
-	pdata->sda_pin = of_get_gpio(np, 0);
-	pdata->scl_pin = of_get_gpio(np, 1);
+	*sda_pin = of_get_gpio(np, 0);
+	*scl_pin = of_get_gpio(np, 1);
 
-	if (!gpio_is_valid(pdata->sda_pin) || !gpio_is_valid(pdata->scl_pin)) {
+	if (!gpio_is_valid(*sda_pin) || !gpio_is_valid(*scl_pin)) {
 		pr_err("%s: invalid GPIO pins, sda=%d/scl=%d\n",
-		       np->full_name, pdata->sda_pin, pdata->scl_pin);
+		       np->full_name, *sda_pin, *scl_pin);
 		return -ENODEV;
 	}
 
+	return 0;
+}
+
+static void of_i2c_gpio_get_props(struct device_node *np,
+				  struct i2c_gpio_platform_data *pdata)
+{
+	u32 reg;
+
 	of_property_read_u32(np, "i2c-gpio,delay-us", &pdata->udelay);
 
 	if (!of_property_read_u32(np, "i2c-gpio,timeout-ms", &reg))
@@ -113,8 +119,6 @@ static int of_i2c_gpio_probe(struct devi
 		of_property_read_bool(np, "i2c-gpio,scl-open-drain");
 	pdata->scl_is_output_only =
 		of_property_read_bool(np, "i2c-gpio,scl-output-only");
-
-	return 0;
 }
 
 static int i2c_gpio_probe(struct platform_device *pdev)
@@ -123,31 +127,52 @@ static int i2c_gpio_probe(struct platfor
 	struct i2c_gpio_platform_data *pdata;
 	struct i2c_algo_bit_data *bit_data;
 	struct i2c_adapter *adap;
+	unsigned int sda_pin, scl_pin;
 	int ret;
 
-	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
-	if (!priv)
-		return -ENOMEM;
-	adap = &priv->adap;
-	bit_data = &priv->bit_data;
-	pdata = &priv->pdata;
-
+	/* First get the GPIO pins; if it fails, we'll defer the probe. */
 	if (pdev->dev.of_node) {
-		ret = of_i2c_gpio_probe(pdev->dev.of_node, pdata);
+		ret = of_i2c_gpio_get_pins(pdev->dev.of_node,
+					   &sda_pin, &scl_pin);
 		if (ret)
 			return ret;
 	} else {
 		if (!pdev->dev.platform_data)
 			return -ENXIO;
-		memcpy(pdata, pdev->dev.platform_data, sizeof(*pdata));
+		pdata = pdev->dev.platform_data;
+		sda_pin = pdata->sda_pin;
+		scl_pin = pdata->scl_pin;
 	}
 
-	ret = gpio_request(pdata->sda_pin, "sda");
-	if (ret)
+	ret = gpio_request(sda_pin, "sda");
+	if (ret) {
+		if (ret == -EINVAL)
+			ret = -EPROBE_DEFER;	/* Try again later */
 		goto err_request_sda;
-	ret = gpio_request(pdata->scl_pin, "scl");
-	if (ret)
+	}
+	ret = gpio_request(scl_pin, "scl");
+	if (ret) {
+		if (ret == -EINVAL)
+			ret = -EPROBE_DEFER;	/* Try again later */
 		goto err_request_scl;
+	}
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv) {
+		ret = -ENOMEM;
+		goto err_add_bus;
+	}
+	adap = &priv->adap;
+	bit_data = &priv->bit_data;
+	pdata = &priv->pdata;
+
+	if (pdev->dev.of_node) {
+		pdata->sda_pin = sda_pin;
+		pdata->scl_pin = scl_pin;
+		of_i2c_gpio_get_props(pdev->dev.of_node, pdata);
+	} else {
+		memcpy(pdata, pdev->dev.platform_data, sizeof(*pdata));
+	}
 
 	if (pdata->sda_is_open_drain) {
 		gpio_direction_output(pdata->sda_pin, 1);
@@ -211,9 +236,9 @@ static int i2c_gpio_probe(struct platfor
 	return 0;
 
 err_add_bus:
-	gpio_free(pdata->scl_pin);
+	gpio_free(scl_pin);
 err_request_scl:
-	gpio_free(pdata->sda_pin);
+	gpio_free(sda_pin);
 err_request_sda:
 	return ret;
 }


-- 
Jean Delvare