linux-kernel - [PATCH v2] gpio: Return EPROBE_DEFER if gc->to

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Date:   Tue, 19 Oct 2021 03:35:04 +0530
From:   Shreeya Patel <shreeya.patel@...labora.com>
To:     linus.walleij@...aro.org, bgolaszewski@...libre.com,
        wsa@...nel.org, krisman@...labora.com,
        sebastian.reichel@...labora.com
Cc:     kernel@...labora.com, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        Shreeya Patel <shreeya.patel@...labora.com>
Subject: [PATCH v2] gpio: Return EPROBE_DEFER if gc->to_irq is NULL

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.

References :-
https://bugzilla.kernel.org/show_bug.cgi?id=209413
https://github.com/Syniurge/i2c-amd-mp2/issues/3

Signed-off-by: Shreeya Patel <shreeya.patel@...labora.com>

---
Changes in v2
  - Add a condition to check for irq chip to avoid bogus error.

---
 drivers/gpio/gpiolib.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 27c07108496d..12c088706167 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -3084,6 +3084,14 @@ int gpiod_to_irq(const struct gpio_desc *desc)
 
 		return retirq;
 	}
+	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;
+	}
+
 	return -ENXIO;
 }
 EXPORT_SYMBOL_GPL(gpiod_to_irq);
-- 
2.30.2