Re: Replacing global GPIO numbers in sysfs with hardware offsets

[Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>]

Hi Bartosz et al,

On Sun, 2 Feb 2025 at 13:46, Bartosz Golaszewski <brgl@xxxxxxxx> wrote:
> I floated an idea of introducing a backward compatible change to sysfs
> that would allow users to identify GPIOs by the label of their parent
> chip and the hardware offset of the line within that chip (like what
> we do for the character device) in the form of the export/unexport
> pair of attributes inside the gpiochipXYZ directory associated with
> given controller. These attributes, unlike the "global"
> export/unexport would take the hardware offset and create the line
> directory within the chip directory of which the layout would be the
> same as that of its global counterpart (in fact: it could point to the
> same directory in sysfs as a single line can only be requested once).
>
> We could then encourage users to switch to using the chip-local
> exports and eventually at least remove the global export/unexport pair
> if we cannot make the entire sysfs class go away.
>
> Please let me know what you think about it?

I like it. Note that there are other caveats of the old API to
take into account...

The other thing to consider is why people are playing with GPIOs
directly: do they lack hardware descriptions? Or do they lack proper
Linux drivers for their use cases? Something else (people brought up
testing random pins, or plugging random things into a Pi)?

Personally, I still use the GPIO sysfs interface to control my board
farm (opto-couplers for reset, wake-up, and key-presses; MOSFETs
for power).  If appropriate drivers would be available, incl. their
own sysfs APIs, I could use that instead (technically I can already
describe opto-couplers using gpio-leds, and be done with it ;-)

Do we need (simple) driver(s) for relays, solenoids, motors?
E.g. gpio-actuator?
A more advanced example would be an H-bridge motor driver, combining
GPIO and (optionally) PWM.
Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds