linux-kernel - [PATCH] pca953x: Added mutex to fix race condition

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Message-Id: <1296300815-24925-1-git-send-email-stigge@antcom.de>
Date:	Sat, 29 Jan 2011 12:33:35 +0100
From:	stigge@...com.de
To:	bgardner@...tec.com, eric.miao@...vell.com,
	linux-kernel@...r.kernel.org
Cc:	Roland Stigge <stigge@...com.de>
Subject: [PATCH] pca953x: Added mutex to fix race condition

pca953x: Added mutex to fix race condition

This patch adds a mutex to register communication and handling. Without the
mutex, GPIOs didn't switch as expected when toggled in a fast sequence of
status changes of multiple outputs.

Signed-off-by: Roland Stigge <stigge@...com.de>

diff --git a/drivers/gpio/pca953x.c b/drivers/gpio/pca953x.c
index a261972..b473429e 100644
--- a/drivers/gpio/pca953x.c
+++ b/drivers/gpio/pca953x.c
@@ -60,6 +60,7 @@ struct pca953x_chip {
 	unsigned gpio_start;
 	uint16_t reg_output;
 	uint16_t reg_direction;
+	struct mutex i2c_lock;
 
 #ifdef CONFIG_GPIO_PCA953X_IRQ
 	struct mutex irq_lock;
@@ -119,13 +120,17 @@ static int pca953x_gpio_direction_input(struct gpio_chip *gc, unsigned off)
 
 	chip = container_of(gc, struct pca953x_chip, gpio_chip);
 
+	mutex_lock(&chip->i2c_lock);
 	reg_val = chip->reg_direction | (1u << off);
 	ret = pca953x_write_reg(chip, PCA953X_DIRECTION, reg_val);
 	if (ret)
-		return ret;
+		goto exit;
 
 	chip->reg_direction = reg_val;
-	return 0;
+	ret = 0;
+exit:
+	mutex_unlock(&chip->i2c_lock);
+	return ret;
 }
 
 static int pca953x_gpio_direction_output(struct gpio_chip *gc,
@@ -137,6 +142,7 @@ static int pca953x_gpio_direction_output(struct gpio_chip *gc,
 
 	chip = container_of(gc, struct pca953x_chip, gpio_chip);
 
+	mutex_lock(&chip->i2c_lock);
 	/* set output level */
 	if (val)
 		reg_val = chip->reg_output | (1u << off);
@@ -145,7 +151,7 @@ static int pca953x_gpio_direction_output(struct gpio_chip *gc,
 
 	ret = pca953x_write_reg(chip, PCA953X_OUTPUT, reg_val);
 	if (ret)
-		return ret;
+		goto exit;
 
 	chip->reg_output = reg_val;
 
@@ -153,10 +159,13 @@ static int pca953x_gpio_direction_output(struct gpio_chip *gc,
 	reg_val = chip->reg_direction & ~(1u << off);
 	ret = pca953x_write_reg(chip, PCA953X_DIRECTION, reg_val);
 	if (ret)
-		return ret;
+		goto exit;
 
 	chip->reg_direction = reg_val;
-	return 0;
+	ret = 0;
+exit:
+	mutex_unlock(&chip->i2c_lock);
+	return ret;
 }
 
 static int pca953x_gpio_get_value(struct gpio_chip *gc, unsigned off)
@@ -167,7 +176,9 @@ static int pca953x_gpio_get_value(struct gpio_chip *gc, unsigned off)
 
 	chip = container_of(gc, struct pca953x_chip, gpio_chip);
 
+	mutex_lock(&chip->i2c_lock);
 	ret = pca953x_read_reg(chip, PCA953X_INPUT, &reg_val);
+	mutex_unlock(&chip->i2c_lock);
 	if (ret < 0) {
 		/* NOTE:  diagnostic already emitted; that's all we should
 		 * do unless gpio_*_value_cansleep() calls become different
@@ -187,6 +198,7 @@ static void pca953x_gpio_set_value(struct gpio_chip *gc, unsigned off, int val)
 
 	chip = container_of(gc, struct pca953x_chip, gpio_chip);
 
+	mutex_lock(&chip->i2c_lock);
 	if (val)
 		reg_val = chip->reg_output | (1u << off);
 	else
@@ -194,9 +206,11 @@ static void pca953x_gpio_set_value(struct gpio_chip *gc, unsigned off, int val)
 
 	ret = pca953x_write_reg(chip, PCA953X_OUTPUT, reg_val);
 	if (ret)
-		return;
+		goto exit;
 
 	chip->reg_output = reg_val;
+exit:
+	mutex_unlock(&chip->i2c_lock);
 }
 
 static void pca953x_setup_gpio(struct pca953x_chip *chip, int gpios)
@@ -517,6 +531,8 @@ static int __devinit pca953x_probe(struct i2c_client *client,
 
 	chip->names = pdata->names;
 
+	mutex_init(&chip->i2c_lock);
+
 	/* initialize cached registers from their original values.
 	 * we can't share this chip with another i2c master.
 	 */
--
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