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

[Marek Vasut <marex@nabladev.com>]

On 5/13/26 11:13 AM, Bartosz Golaszewski 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.

Shouldn't this polarity inversion be handled by DT GPIO_ACTIVE_* flag ?

> Fixes: e992d54c6f97 ("gpio: shared-proxy: implement the shared GPIO proxy driver")
> Reported-by: Marek Vasut <marex@nabladev.com>
> Closes: https://lore.kernel.org/all/20260511163518.51104-1-marex@nabladev.com/
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
> ---
> Hi Marek!
> 
> Please see if you can make your setup work with shared GPIOs with this
> patch. You need to enable CONFIG_HAVE_SHARED_GPIOS on your platform.

Why can this shared GPIO not be enabled generically for any GPIO 
controller ?

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