Re: [PATCH RFC] gpio: define gpio-init nodes to initialize pins similar to hogs

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Mon, Sep 9, 2019 at 11:59 AM Uwe Kleine-König
<u.kleine-koenig@xxxxxxxxxxxxxx> wrote:

> Sometimes it is handy to be able to easily define a "safe" state for a
> GPIO. This might for example be used to ensure that an ethernet phy is
> properly reset during startup or just that all pins have a defined state
> to minimize leakage current. As such a pin must be requestable (and
> changable) by a device driver, a gpio-hog cannot be used.
>
> So define a GPIO initializer with a syntax identical to a GPIO hog just
> using "gpio-init" as identifier instead of "gpio-hog".
>
> The usage I have in mind (and also implemented in a custom patch stack
> on top of barebox already) is targeting the bootloader and not
> necessarily Linux as such an boot-up initialisation should be done as
> early as possible.
>
> Not-yet-signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> ---
> Hello,
>
> maybe it also makes sense to use "gpio-safe"? Maybe it (then) makes
> sense to reset the gpio in the indicated state after it is released?
>
> Also it might be beneficial to make the wording more explicit in the
> description and for example tell that only one of gpio-hog and gpio-init
> must be provided.

It's no secret that I am in favor of this approach, as I like consistency
with the hogs.

The DT people have been against, as they prefer something like an
initial array of values akin to gpio-names IIRC. But this is a good
time for them to speak up.

Yours,
Linus Walleij