Re: [RFC] GPIO User I/O

[Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>]

Hi Drew,

On Tue, Jul 7, 2020 at 10:39 AM Drew Fustini <pdp7pdp7@xxxxxxxxx> wrote:
> On Tue, Jul 7, 2020, 09:18 Rodolfo Giometti <giometti@xxxxxxxxxxxx> wrote:
>> On 06/07/2020 23:00, Geert Uytterhoeven wrote:
>> > On Mon, Jul 6, 2020 at 10:38 PM Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
>> >> On Mon, Jul 6, 2020 at 5:33 PM Rodolfo Giometti <giometti@xxxxxxxxxxxx> wrote:
>> >>>> With Geert's GPIO aggregator userspace and device tree can conjure
>> >>>> special per-usecase gpio chips as pointed out by Drew: this is
>> >>>> very useful when you want some kernel-managed yet
>> >>>> usecase-specific GPIO lines in a special "container" chip.
>> >>>> To me this is the best of two worlds. (Kernelspace and userspace.)
>> >>>
>> >>> Maybe this is the "best of two worlds" as you say but the problem is that board
>> >>> manufactures need a way to well-define how a GPIO line must be used for within
>> >>> the device-tree and without the need of patches! In this point of view neither
>> >>> the "driver_override" way nor adding a compatible value to
>> >>> gpio_aggregator_dt_ids[] can help (this last solution requires a patch for each
>> >>> board!). That's why at the moment they prefer not specify these GPIO lines at
>> >>> all or (improperly) use the gpio-leds and gpio-uinput interfaces to keep it
>> >>> simple...
>> >>
>> >> I think the idea is to add a very generic DT compatible to the
>> >> gpio_aggregator_dt_ids[]. That way, any DT can use the aggregator
>> >> to create a new chip with named lines etc.
>> >>
>> >> But Geert can speak of that.
>> >
>> > The idea is to describe the real device in DT, and add it's compatible value
>> > to gpio_aggregator_dt_ids[], or enable support for it dynamically using
>> > driver_override.
>> > The former indeed requires modifying the driver.
>>
>> I see.
>>
>> > Note that if you ever want to write a pure kernelspace driver, you do need
>> > a proper compatible value anyway.
>>
>> OK, but for our purposes we need just one compatible value.
>>
>> > I do agree that it's annoying to have "gpio-leds", but not "gpio-motors"
>> > or "gpio-relays".  However, you can always propose bindings for the
>> > latter, and, when they have been accepted, add those compatible
>> > values to upstream gpio_aggregator_dt_ids[].
>>
>> Having gpio-uio with proper names within it as motor0, motor1, relay0, etc. as
>> in my solution would be suffice. However, after these discussions, are there any
>> chances my patch (with needed modifications and documentation) may be accepted? :)
>
>
> Hi, I would like to clarify my understanding of what gpio-uio.
>
> Is there something in mainline that already uses that binding?

No there isn't.

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