linux-kernel - Re: [PATCH v7 08/10] i2c: of-prober: Add GPIO support to simple helpers

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Message-ID: <CAD=FV=Wv1uFmxFsaxT9tY=-fwnPsXDjnabNxQ-cK3hm2a9Wo7A@mail.gmail.com>
Date: Mon, 23 Sep 2024 12:11:49 -0700
From: Doug Anderson <dianders@...omium.org>
To: Chen-Yu Tsai <wenst@...omium.org>
Cc: Rob Herring <robh@...nel.org>, Saravana Kannan <saravanak@...gle.com>, 
	Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Wolfram Sang <wsa@...nel.org>, 
	Benson Leung <bleung@...omium.org>, Tzung-Bi Shih <tzungbi@...nel.org>, 
	Mark Brown <broonie@...nel.org>, Liam Girdwood <lgirdwood@...il.com>, 
	chrome-platform@...ts.linux.dev, devicetree@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, Johan Hovold <johan@...nel.org>, 
	Jiri Kosina <jikos@...nel.org>, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
	linux-i2c@...r.kernel.org
Subject: Re: [PATCH v7 08/10] i2c: of-prober: Add GPIO support to simple helpers

Hi,

On Tue, Sep 17, 2024 at 5:41 AM Chen-Yu Tsai <wenst@...omium.org> wrote:
>
> > > +static void i2c_of_probe_simple_disable_gpio(struct device *dev, struct i2c_of_probe_simple_ctx *ctx)
> > > +{
> > > +       if (!ctx->gpiod)
> > > +               return;
> > > +
> > > +       dev_dbg(dev, "Setting GPIO to input\n");
> > > +
> > > +       gpiod_direction_input(ctx->gpiod);
> >
> > This is weird. Why set it to input?
>
> It seemed to me this would be more like the initial state, without knowing
> the actual initial state.

In this case, though, you're trying to turn off the resource, not
trying to get back to the initial state. IMO deasserting the GPIO is
the way to do this. If the output needs to make it an input in this
case then it can use some type of open drain mode.


> > I would also say: given that you're providing a parameter anyway and
> > you're giving the GPIO name, can you please move away from the "raw"
> > values and move to "logical" values?
>
> I disagree. When hardware engineers design for swappable components, they
> likely look at the electrical compatibility of them. In this case, an
> active-high "enable" pin is electrically compatible with an active-low
> "reset" pin. If we use the logical value here, then we would need more
> logic to know when the logical polarity has to be reversed.
>
> Note that this doesn't work for components that are electrically
> incompatible. But in that case a lot more board dependent code would be
> needed anyway.

As we talked about in person, that made sense in the previous version
of the patch where you were looking for all GPIOs willy-nilly. Now
you'll be specifically asking for a GPIO by name and we should honor
the "active high" or "active low" nature of it.

-Doug