Re: [PATCH] gpio: shared: make the voting mechanism adaptable

[Linus Walleij]

On Wed, May 13, 2026 at 11:14 AM Bartosz Golaszewski
<bartosz.golaszewski@xxxxxxxxxxxxxxxx> wrote:

> The current voting mechanism in GPIO shared proxy assumes that "low" is
> always the default value and users can only vote for driving the GPIO
> "high" in which case it will remain high as long as there's at least one
> user voting.
>
> This makes it impossible to use the automatic sharing management for
> certain use-cases such as the write-protect GPIOs of EEPROMs which are
> requested "high" and driven "low" to enable writing. In this case, if
> the WP GPIO is shared by multiple EEPROMs, and at least one of them
> wants to enable writing, the pin must be set to "low".
>
> Modify the voting heuristic to assume the value set by the first user on
> request to be the "default" and subseqent calls to gpiod_set_value()
> will constitute votes for a change of the value to the opposite. In the
> wp-gpios case it will mean that the nvmem core requests the GPIO as
> "out-high" for all EEPROMs sharing the pin, and when one of them wants
> to write, the pin will be driven low, enabling it.
>
> Fixes: e992d54c6f97 ("gpio: shared-proxy: implement the shared GPIO proxy driver")
> Reported-by: Marek Vasut <marex@xxxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/20260511163518.51104-1-marex@xxxxxxxxxxxx/
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxxxxxxxx>

I like this idea.
Reviewed-by: Linus Walleij <linusw@xxxxxxxxxx>

BTW was this "voting" system inspired by the hardware "vote" thing
that Qualcomm is using for power management? That's the only place
I've seen it before.

Yours,
Linus Walleij