Patch "gpio: Return EPROBE_DEFER if gc->to_irq is NULL" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    gpio: Return EPROBE_DEFER if gc->to_irq is NULL

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     gpio-return-eprobe_defer-if-gc-to_irq-is-null.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 5ca3f93bdf8040630d378a942f6f88c4d208b2dc
Author: Shreeya Patel <shreeya.patel@xxxxxxxxxxxxx>
Date:   Thu Feb 17 01:56:55 2022 +0530

    gpio: Return EPROBE_DEFER if gc->to_irq is NULL
    
    [ Upstream commit ae42f9288846353982e2eab181fb41e7fd8bf60f ]
    
    We are racing the registering of .to_irq when probing the
    i2c driver. This results in random failure of touchscreen
    devices.
    
    Following explains the race condition better.
    
    [gpio driver] gpio driver registers gpio chip
    [gpio consumer] gpio is acquired
    [gpio consumer] gpiod_to_irq() fails with -ENXIO
    [gpio driver] gpio driver registers irqchip
    gpiod_to_irq works at this point, but -ENXIO is fatal
    
    We could see the following errors 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.
    Returning -EPROBE_DEFER would be the first step towards avoiding
    the failure of devices due to the race in registration of .to_irq.
    Final solution to this issue would be to avoid using gc irq members
    until they are fully initialized.
    
    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@xxxxxxxxxx>
    Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
    Reported-by: kernel test robot <lkp@xxxxxxxxx>
    Signed-off-by: Shreeya Patel <shreeya.patel@xxxxxxxxxxxxx>
    Signed-off-by: Bartosz Golaszewski <brgl@xxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index af5bb8fedfea..00526fdd7691 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -3215,6 +3215,16 @@ 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);