[PATCH v4] gpio: Return EPROBE_DEFER if gc->to_irq is NULL

[Shreeya Patel <shreeya.patel@collabora.com>]

We are racing the registering of .to_irq when probing the
i2c driver. This results in random failure of touchscreen
devices.

Following errors could be seen in dmesg logs when gc->to_irq is NULL

[2.101857] i2c_hid i2c-FTS3528:00: HID over i2c has not been provided an Int IRQ
[2.101953] i2c_hid: probe of i2c-FTS3528:00 failed with error -22

To avoid this situation, defer probing until to_irq is registered.

This issue has been reported many times in past and people have been
using workarounds like changing the pinctrl_amd to built-in instead
of loading it as a module or by adding a softdep for pinctrl_amd into
the config file.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=209413
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Shreeya Patel <shreeya.patel@collabora.com>

---
Changes in v4
  - Remove blank line and make the first letter of the sentence
capital.

Changes in v3
  - Fix the error reported by kernel test robot.

Changes in v2
  - Add a condition to check for irq chip to avoid bogus error.
---
 drivers/gpio/gpiolib.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index abfbf546d159..7b3f7f4d1d06 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -3111,6 +3111,16 @@ int gpiod_to_irq(const struct gpio_desc *desc)
 
 		return retirq;
 	}
+#ifdef CONFIG_GPIOLIB_IRQCHIP
+	if (gc->irq.chip) {
+		/*
+		 * Avoid race condition with other code, which tries to lookup
+		 * an IRQ before the irqchip has been properly registered,
+		 * i.e. while gpiochip is still being brought up.
+		 */
+		return -EPROBE_DEFER;
+	}
+#endif
 	return -ENXIO;
 }
 EXPORT_SYMBOL_GPL(gpiod_to_irq);
-- 
2.30.2