gpio: zynq: protect direction in/out with a spinlock

Fix race condition when changing the direction (in/out) of the GPIO pin.
The read-modify-write sequence (as coded in the driver) isn't atomic and
requires synchronization (spinlock).
Signed-off-by: Glenn Langedock <Glenn.Langedock@barco.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Srinivas Neeli <srinivas.neeli@xilinx.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/gpio-zynq.c

@@ -10,6 +10,7 @@
 #include <linux/gpio/driver.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
+#include <linux/spinlock.h>
 #include <linux/io.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
@@ -116,6 +117,7 @@ struct gpio_regs {
  * @irq:	interrupt for the GPIO device
  * @p_data:	pointer to platform data
  * @context:	context registers
+ * @dirlock:	lock used for direction in/out synchronization
  */
 struct zynq_gpio {
 	struct gpio_chip chip;
@@ -124,6 +126,7 @@ struct zynq_gpio {
 	int irq;
 	const struct zynq_platform_data *p_data;
 	struct gpio_regs context;
+	spinlock_t dirlock; /* lock */
 };
 
 /**
@@ -297,6 +300,7 @@ static int zynq_gpio_dir_in(struct gpio_chip *chip, unsigned int pin)
 {
 	u32 reg;
 	unsigned int bank_num, bank_pin_num;
+	unsigned long flags;
 	struct zynq_gpio *gpio = gpiochip_get_data(chip);
 
 	zynq_gpio_get_bank_pin(pin, &bank_num, &bank_pin_num, gpio);
@@ -310,9 +314,11 @@ static int zynq_gpio_dir_in(struct gpio_chip *chip, unsigned int pin)
 		return -EINVAL;
 
 	/* clear the bit in direction mode reg to set the pin as input */
+	spin_lock_irqsave(&gpio->dirlock, flags);
 	reg = readl_relaxed(gpio->base_addr + ZYNQ_GPIO_DIRM_OFFSET(bank_num));
 	reg &= ~BIT(bank_pin_num);
 	writel_relaxed(reg, gpio->base_addr + ZYNQ_GPIO_DIRM_OFFSET(bank_num));
+	spin_unlock_irqrestore(&gpio->dirlock, flags);
 
 	return 0;
 }
@@ -334,11 +340,13 @@ static int zynq_gpio_dir_out(struct gpio_chip *chip, unsigned int pin,
 {
 	u32 reg;
 	unsigned int bank_num, bank_pin_num;
+	unsigned long flags;
 	struct zynq_gpio *gpio = gpiochip_get_data(chip);
 
 	zynq_gpio_get_bank_pin(pin, &bank_num, &bank_pin_num, gpio);
 
 	/* set the GPIO pin as output */
+	spin_lock_irqsave(&gpio->dirlock, flags);
 	reg = readl_relaxed(gpio->base_addr + ZYNQ_GPIO_DIRM_OFFSET(bank_num));
 	reg |= BIT(bank_pin_num);
 	writel_relaxed(reg, gpio->base_addr + ZYNQ_GPIO_DIRM_OFFSET(bank_num));
@@ -347,6 +355,7 @@ static int zynq_gpio_dir_out(struct gpio_chip *chip, unsigned int pin,
 	reg = readl_relaxed(gpio->base_addr + ZYNQ_GPIO_OUTEN_OFFSET(bank_num));
 	reg |= BIT(bank_pin_num);
 	writel_relaxed(reg, gpio->base_addr + ZYNQ_GPIO_OUTEN_OFFSET(bank_num));
+	spin_unlock_irqrestore(&gpio->dirlock, flags);
 
 	/* set the state of the pin */
 	zynq_gpio_set_value(chip, pin, state);
@@ -885,6 +894,8 @@ static int zynq_gpio_probe(struct platform_device *pdev)
 		return ret;
 	}
 
+	spin_lock_init(&gpio->dirlock);
+
 	pm_runtime_set_active(&pdev->dev);
 	pm_runtime_enable(&pdev->dev);
 	ret = pm_runtime_get_sync(&pdev->dev);