realtek: don't unmask non-maskable GPIO IRQs

On uniprocessor builds, for_each_cpu(cpu, mask) will assume 'mask'
always contains exactly one CPU, and ignore the actual mask contents.
This causes the loop to run, even when it shouldn't on an empty mask,
and tries to access an uninitialised pointer.

Fix this by wrapping the loop in a cpumask_empty() check, to ensure it
will not run on uniprocessor builds if the CPU mask is empty.

Fixes: af6cd37 ("realtek: replace RTL93xx GPIO patches")
Reported-by: INAGAKI Hiroshi <musashino.open@gmail.com>
Reported-by: Robert Marko <robimarko@gmail.com>
Tested-by: Robert Marko <robimarko@gmail.com>
Signed-off-by: Sander Vanheule <sander@svanheule.net>

target/linux/realtek/patches-5.10/316-otto-gpio-uniprocessor-irq-mask.patch

@@ -0,0 +1,29 @@
+--- a/drivers/gpio/gpio-realtek-otto.c
++++ b/drivers/gpio/gpio-realtek-otto.c
+@@ -304,6 +304,7 @@ static int realtek_gpio_irq_set_affinity
+ static int realtek_gpio_irq_init(struct gpio_chip *gc)
+ {
+ 	struct realtek_gpio_ctrl *ctrl = gpiochip_get_data(gc);
++	void __iomem *irq_cpu_mask;
+ 	unsigned int port;
+ 	int cpu;
+
+@@ -311,8 +312,16 @@ static int realtek_gpio_irq_init(struct
+ 		realtek_gpio_write_imr(ctrl, port, 0, 0);
+ 		realtek_gpio_clear_isr(ctrl, port, GENMASK(7, 0));
+
+-		for_each_cpu(cpu, &ctrl->cpu_irq_maskable)
+-			iowrite8(GENMASK(7, 0), realtek_gpio_irq_cpu_mask(ctrl, port, cpu));
++		/*
++		 * Uniprocessor builds assume a mask always contains one CPU,
++		 * so only start the loop if we have at least one maskable CPU.
++		 */
++		if(!cpumask_empty(&ctrl->cpu_irq_maskable)) {
++			for_each_cpu(cpu, &ctrl->cpu_irq_maskable) {
++				irq_cpu_mask = realtek_gpio_irq_cpu_mask(ctrl, port, cpu);
++				iowrite8(GENMASK(7, 0), irq_cpu_mask);
++			}
++		}
+ 	}
+
+ 	return 0;