[PATCH v2] gpio: vf610: add locking to gpio direction functions

[Johan Korsnes <johan.korsnes@xxxxxxxxxxxxx>]

Add locking to `vf610_gpio_direction_input|output()` functions. Without
this locking, a race condition exists between concurrent calls to these
functions, potentially leading to incorrect GPIO direction settings.

To verify the correctness of this fix, a `trylock` patch was applied,
where after a couple of reboots the race was confirmed. I.e., one user
had to wait before acquiring the lock. With this patch the race has not
been encountered. It's worth mentioning that any type of debugging
(printing, tracing, etc.) would "resolve"/hide the issue.

Signed-off-by: Johan Korsnes <johan.korsnes@xxxxxxxxxxxxx>
Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
Reviewed-by: Haibo Chen <haibo.chen@xxxxxxx>
Cc: Bartosz Golaszewski <brgl@xxxxxxxx>

---

v2
 - Added description on correcctness to commit text
 - Added Reviewed-by from Walleij and Haibo
---
 drivers/gpio/gpio-vf610.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpio/gpio-vf610.c b/drivers/gpio/gpio-vf610.c
index c4f34a347cb6..3527487d42c8 100644
--- a/drivers/gpio/gpio-vf610.c
+++ b/drivers/gpio/gpio-vf610.c
@@ -36,6 +36,7 @@ struct vf610_gpio_port {
 	struct clk *clk_port;
 	struct clk *clk_gpio;
 	int irq;
+	spinlock_t lock; /* protect gpio direction registers */
 };
 
 #define GPIO_PDOR		0x00
@@ -121,12 +122,15 @@ static int vf610_gpio_direction_input(struct gpio_chip *chip, unsigned int gpio)
 {
 	struct vf610_gpio_port *port = gpiochip_get_data(chip);
 	u32 mask = BIT(gpio);
+	unsigned long flags;
 	u32 val;
 
 	if (port->sdata->have_paddr) {
+		spin_lock_irqsave(&port->lock, flags);
 		val = vf610_gpio_readl(port->gpio_base + GPIO_PDDR);
 		val &= ~mask;
 		vf610_gpio_writel(val, port->gpio_base + GPIO_PDDR);
+		spin_unlock_irqrestore(&port->lock, flags);
 	}
 
 	return pinctrl_gpio_direction_input(chip, gpio);
@@ -137,14 +141,17 @@ static int vf610_gpio_direction_output(struct gpio_chip *chip, unsigned int gpio
 {
 	struct vf610_gpio_port *port = gpiochip_get_data(chip);
 	u32 mask = BIT(gpio);
+	unsigned long flags;
 	u32 val;
 
 	vf610_gpio_set(chip, gpio, value);
 
 	if (port->sdata->have_paddr) {
+		spin_lock_irqsave(&port->lock, flags);
 		val = vf610_gpio_readl(port->gpio_base + GPIO_PDDR);
 		val |= mask;
 		vf610_gpio_writel(val, port->gpio_base + GPIO_PDDR);
+		spin_unlock_irqrestore(&port->lock, flags);
 	}
 
 	return pinctrl_gpio_direction_output(chip, gpio);
@@ -297,6 +304,7 @@ static int vf610_gpio_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	port->sdata = device_get_match_data(dev);
+	spin_lock_init(&port->lock);
 
 	dual_base = port->sdata->have_dual_base;
 
-- 
2.43.0