Re: [PATCH v5] gpio: Return EPROBE_DEFER if gc->to_irq is NULL

[Bartosz Golaszewski <brgl@bgdev.pl>]

On Wed, Feb 16, 2022 at 9:27 PM Shreeya Patel
<shreeya.patel@collabora.com> wrote:
>
> 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@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 v5
>   - Improve explanation in commit message and sending it to the correct
> email address.
>
> 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 3859911b61e9..a3d14277f17c 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -3147,6 +3147,16 @@ 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
>

Queued for fixes, thanks!

Bart