gpio: mxc: Protect GPIO irqchip RMW with bgpio spinlock

The driver currently performs register read-modify-write without locking
in its irqchip part, this could lead to a race condition when configuring
interrupt mode setting. Add the missing bgpio spinlock lock/unlock around
the register read-modify-write.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Fixes: 07bd1a6c ("MXC arch: Add gpio support for the whole platform")
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

drivers/gpio/gpio-mxc.c

@@ -18,6 +18,7 @@
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/slab.h>
+#include <linux/spinlock.h>
 #include <linux/syscore_ops.h>
 #include <linux/gpio/driver.h>
 #include <linux/of.h>
@@ -159,6 +160,7 @@ static int gpio_set_irq_type(struct irq_data *d, u32 type)
 {
 	struct irq_chip_generic *gc = irq_data_get_irq_chip_data(d);
 	struct mxc_gpio_port *port = gc->private;
+	unsigned long flags;
 	u32 bit, val;
 	u32 gpio_idx = d->hwirq;
 	int edge;
@@ -197,6 +199,8 @@ static int gpio_set_irq_type(struct irq_data *d, u32 type)
 		return -EINVAL;
 	}
 
+	raw_spin_lock_irqsave(&port->gc.bgpio_lock, flags);
+
 	if (GPIO_EDGE_SEL >= 0) {
 		val = readl(port->base + GPIO_EDGE_SEL);
 		if (edge == GPIO_INT_BOTH_EDGES)
@@ -217,15 +221,20 @@ static int gpio_set_irq_type(struct irq_data *d, u32 type)
 	writel(1 << gpio_idx, port->base + GPIO_ISR);
 	port->pad_type[gpio_idx] = type;
 
+	raw_spin_unlock_irqrestore(&port->gc.bgpio_lock, flags);
+
 	return 0;
 }
 
 static void mxc_flip_edge(struct mxc_gpio_port *port, u32 gpio)
 {
 	void __iomem *reg = port->base;
+	unsigned long flags;
 	u32 bit, val;
 	int edge;
 
+	raw_spin_lock_irqsave(&port->gc.bgpio_lock, flags);
+
 	reg += GPIO_ICR1 + ((gpio & 0x10) >> 2); /* lower or upper register */
 	bit = gpio & 0xf;
 	val = readl(reg);
@@ -243,6 +252,8 @@ static void mxc_flip_edge(struct mxc_gpio_port *port, u32 gpio)
 		return;
 	}
 	writel(val | (edge << (bit << 1)), reg);
+
+	raw_spin_unlock_irqrestore(&port->gc.bgpio_lock, flags);
 }
 
 /* handle 32 interrupts in one status register */