Re: [PATCH] gpiolib: TODO: add an item about GPIO safe-state

[Rob Herring <robh+dt@kernel.org>]

On Fri, Sep 16, 2022 at 8:12 AM Linus Walleij <linus.walleij@linaro.org> wrote:
>
> On Fri, Sep 16, 2022 at 9:11 AM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>
> > Of course we were not the first ones to think about it...
>
> :D
>
> > I'll read through it later. Was there any particular reason why this
> > never made its way into the kernel?
>
> Inability to drive through a DT binding that was acceptable for the
> DT binding maintainers.

AFAICT, this came up briefly in 2015, then 2017, then 2019. (You're a
year late this time.) A nice regular pattern to not get something
upstream...

> A good idea to get it passed I think would be to ask Rob (with some
> examples) how he thinks it should look and finalize the bindings
> before coding.

My issue was more that by the time the kernel or even bootloader runs,
quite a bit of time has passed given all the firmware that runs
nowadays. Doesn't a safe state need to be set as early as possible?
Like probably before anything using DT?

A node per GPIO could end up being a lot of nodes and I can certainly
see folks just initializing every GPIO. That would be a lot of bloat.
As I see it we need 4 bits per line: direction, state(high/low), pull
up/down/none.

Finally, don't non-GPIO pins need the same thing? You don't want a
default output driving what needs to be an input. Of course, a good
h/w designer wouldn't design such a thing.

Rob