Re: [PATCH v2] leds: Mark GPIO LED trigger broken

[Lee Jones <lee@xxxxxxxxxx>]

On Tue, 14 Mar 2023, Linus Walleij wrote:

> The GPIO LED trigger exposes a userspace ABI where a user
> can echo a GPIO number from the global GPIO numberspace into
> a file that will trigger a certain LED when active.
>
> This is problematic because the global GPIO numberspace is
> inherently instable. The trigger came about at a time when
> systems had one GPIO controller that defined hard-wired
> GPIOs numbered 0..N and this number space was stable.
>
> We have since moved to dynamic allocation of GPIO numbers
> and there is no real guarantee that a GPIO number will stay
> consistent even across a reboot: consider a USB attached
> GPIO controller for example. Or two. Or the effect of
> probe order after adding -EPROBE_DEFER to the kernel.
>
> The trigger was added to support keypad LEDs on the Nokia
> n810 from the GPIO event when a user slides up/down the
> keypad. This is arch/arm/boot/dts/omap2420-n810.dts.
> A userspace script is needed to activate the trigger.
> This will be broken unless the script was updated recently
> since the OMAP GPIO controller now uses dynamic GPIO
> number allocations.
>
> I want to know that this trigger has active users that
> cannot live without it if we are to continue to support it.
>
> Option if this is really needed: I can develop a new trigger
> that can associate GPIOs with LEDs as triggers using device
> tree, which should also remove the use of userspace custom
> scripts to achieve this and be much more trustworthy, if
> someone with the Nokia n810 or a device with a similar need
> is willing to test it.
>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Tony Lindgren <tony@xxxxxxxxxxx>
> Cc: Felipe Balbi <balbi@xxxxxxxxxx>
> Cc: linux-omap@xxxxxxxxxxxxxxx
> Cc: linux-gpio@xxxxxxxxxxxxxxx
>
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> ---
> ChangeLog v1->v2:
> - Be less intrusive and just mark the feature broken
>   for now.
> ---
>  drivers/leds/trigger/Kconfig | 1 +
>  1 file changed, 1 insertion(+)

Added Pavel's Suggested-by:

Applied, thanks

--
Lee Jones [李琼斯]