Re: [PATCH 1/3] gpiolib: don't use gpiochip_get_direction() when registering a chip

[Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>]

On 25.02.2025 12:56, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
>
> During chip registration we should neither check the return value of
> gc->get_direction() nor hold the SRCU lock when calling it. The former
> is because pin controllers may have pins set to alternate functions and
> return errors from their get_direction() callbacks. That's alright - we
> should default to the safe INPUT state and not bail-out. The latter is
> not needed because we haven't registered the chip yet so there's nothing
> to protect against dynamic removal. In fact: we currently hit a lockdep
> splat. Revert to calling the gc->get_direction() callback directly not
> not checking its value.
>
> Fixes: 9d846b1aebbe ("gpiolib: check the return value of gpio_chip::get_direction()")
> Fixes: e623c4303ed1 ("gpiolib: sanitize the return value of gpio_chip::get_direction()")
> Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/81f890fc-6688-42f0-9756-567efc8bb97a@xxxxxxxxxxx/
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> ---
>   drivers/gpio/gpiolib.c | 20 ++++----------------
>   1 file changed, 4 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index e8678a6c82ea..31d400b10167 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -1082,24 +1082,12 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
>   
>   		desc->gdev = gdev;
>   
> -		if (gc->get_direction && gpiochip_line_is_valid(gc, desc_index)) {
> -			ret = gpiochip_get_direction(gc, desc_index);
> -			if (ret < 0)
> -				/*
> -				 * FIXME: Bail-out here once all GPIO drivers
> -				 * are updated to not return errors in
> -				 * situations that can be considered normal
> -				 * operation.
> -				 */
> -				dev_warn(&gdev->dev,
> -					 "%s: get_direction failed: %d\n",
> -					 __func__, ret);
> -
> -			assign_bit(FLAG_IS_OUT, &desc->flags, !ret);
> -		} else {
> +		if (gc->get_direction && gpiochip_line_is_valid(gc, desc_index))
> +			assign_bit(FLAG_IS_OUT, &desc->flags,
> +				   !gc->get_direction(gc, desc_index));
> +		else
>   			assign_bit(FLAG_IS_OUT,
>   				   &desc->flags, !gc->direction_input);
> -		}
>   	}
>   
>   	ret = of_gpiochip_add(gc);
>
Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland