[PATCH] gpiolib: check if irqchip already has the irq hook replacements

[Hans Verkuil <hverkuil@xxxxxxxxx>]

Some drivers use a single irqchip for multiple gpiochips. As a result the
irqchip hooks are overridden for the first gpiochip that was added, but
for the other gpiochip instances this should not happen again, otherwise
we would go into an infinite recursion.

Check for this, but also log a message that the driver should be fixed
since this is bad practice.

Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
---
Ludovic, can you test this with your unmodified driver? In particular I'd
like to see how many of these messages you get and how they look like in
the kernel log. I think you should get 4 of these messages.

Thanks!

    Hans
---
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index efce534a269b..a29c917b459f 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1859,6 +1859,16 @@ static void gpiochip_set_irq_hooks(struct gpio_chip *gpiochip)
 	}
 	if (WARN_ON(gpiochip->irq.irq_enable))
 		return;
+	/* Check if the irqchip already has this hook... */
+	if (irqchip->irq_enable == gpiochip_irq_enable) {
+		/*
+		 * ...and if so, give a gentle warning that this is bad
+		 * practice.
+		 */
+		chip_info(gpiochip,
+			  "detected irqchip that is shared with multiple gpiochips: please fix the driver.\n");
+		return;
+	}
 	gpiochip->irq.irq_enable = irqchip->irq_enable;
 	gpiochip->irq.irq_disable = irqchip->irq_disable;
 	irqchip->irq_enable = gpiochip_irq_enable;