Re: [PATCH v4 3/4] gpio: shared-proxy: Drive the default value when no votes are cast

[Bartosz Golaszewski]

On Sat, 17 Oct 2026 06:36:04 +0200, Shawn Guo
<shengchao.guo@xxxxxxxxxxxxxxxx> said:
> A consumer that requests a shared line with GPIOD_ASIS never calls
> direction_output(), so def_val keeps its initial value of 0. If the
> line was left high, for instance by the bootloader, a later
> gpiod_set_value(0) from that consumer matches def_val and the proxy
> treats it as withdrawing a vote it never cast. It returns success
> without writing the hardware, and the line stays high.
>
> The consumer has no way to tell. Its request to drive the line low is
> silently ignored until it first votes for high and then withdraws
> that vote.
>
> When the requested value is the default and no votes are
> outstanding, write it to the hardware instead of returning early.
> For lines configured via direction_output() this is a redundant
> write of the value the line already has. With votes outstanding the
> request remains a no-op, as the line must stay at the voted value.
>

Wouldn't this only matter for a line requested as-is? We could avoid the
redundant write if we only did it for such lines instead of for all
unconditionally.

Bart

> Fixes: e992d54c6f97 ("gpio: shared-proxy: implement the shared GPIO proxy driver")
> Assisted-by: LLM
> Signed-off-by: Shawn Guo <shengchao.guo@xxxxxxxxxxxxxxxx>
> ---
>  drivers/gpio/gpio-shared-proxy.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpio/gpio-shared-proxy.c b/drivers/gpio/gpio-shared-proxy.c
> index 24241c981df1..456a3c3dbf71 100644
> --- a/drivers/gpio/gpio-shared-proxy.c
> +++ b/drivers/gpio/gpio-shared-proxy.c
> @@ -81,9 +81,16 @@ gpio_shared_proxy_set_unlocked(struct gpio_shared_proxy_data *proxy, int value)
>  	}
>
>  	/* Desired value is the default. */
> -	if (!proxy->voted_change)
> -		/* We didn't vote for change previously, nothing to do. */
> +	if (!proxy->voted_change) {
> +		/*
> +		 * With no votes outstanding the line should be at the
> +		 * default, but a GPIOD_ASIS line may have been left at the
> +		 * opposite value. Drive it there.
> +		 */
> +		if (!shared_desc->votecnt)
> +			ret = gpiod_set_value_cansleep(desc, shared_desc->def_val);
>  		goto out;
> +	}
>
>  	/* We previously voted for change. */
>  	if (shared_desc->votecnt == 1) {
> --
> 2.43.0
>
>