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

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Message-ID: <CAGXv+5EcxGfdzvarg8hmk1zR9X0s8KUzayQdxfWTrasEGpj=1g@mail.gmail.com>
Date: Tue, 17 Sep 2024 14:41:26 +0200
From: Chen-Yu Tsai <wenst@...omium.org>
To: Doug Anderson <dianders@...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

On Sat, Sep 14, 2024 at 1:49 AM Doug Anderson <dianders@...omium.org> wrote:
>
> Hi,
>
> On Wed, Sep 11, 2024 at 12:29 AM Chen-Yu Tsai <wenst@...omium.org> wrote:
> >
> > +static int i2c_of_probe_simple_set_gpio(struct device *dev, struct i2c_of_probe_simple_ctx *ctx)
> > +{
> > +       int ret;
> > +
> > +       if (!ctx->gpiod)
> > +               return 0;
> > +
> > +       dev_dbg(dev, "Setting GPIO\n");
> > +
> > +       ret = gpiod_direction_output_raw(ctx->gpiod, ctx->opts->gpio_high_to_enable ? 1 : 0);
> > +       if (ret)
> > +               return ret;
> > +
> > +       msleep(ctx->opts->post_reset_deassert_delay_ms);
>
> Like in the previous patch, you need an "if
> (ctx->opts->post_reset_deassert_delay_ms)" before the msleep().

Ack.

> > +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.

> > @@ -347,6 +438,7 @@ int i2c_of_probe_simple_cleanup(struct device *dev, void *data)
> >  {
> >         struct i2c_of_probe_simple_ctx *ctx = data;
> >
> > +       i2c_of_probe_simple_disable_gpio(dev, ctx);
>
> Maybe add a comment before the GPIO call that it's a noop if we found
> something and i2c_of_probe_simple_free_res_early() was already called?
> Otherwise you need to read into the function to understand why this
> doesn't crash if the early call was made. To me, that makes the
> abstraction add confusion instead of simplifying things.

Ack.

> > @@ -92,24 +93,33 @@ int i2c_of_probe_component(struct device *dev, const struct i2c_of_probe_cfg *cf
> >   * struct i2c_of_probe_simple_opts - Options for simple I2C component prober callbacks
> >   * @res_node_compatible: Compatible string of device node to retrieve resources from.
> >   * @supply_name: Name of regulator supply.
> > + * @gpio_name: Name of GPIO.
>
> Talk about the fact that gpio_name can be NULL or an empty string and
> that they mean different things.

Ack.

> >   * @post_power_on_delay_ms: Delay in ms after regulators are powered on. Passed to msleep().
> > + * @post_reset_deassert_delay_ms: Delay in ms after GPIOs are set. Passed to msleep().
> > + * @gpio_high_to_enable: %true if GPIO should be set to electrical high to enable component.
>
> Now that you've added the GPIOs and more delays, the description of
> this structure needs to list exactly what the power sequence your
> simple functions assume.

Ack.

> 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.


ChenYu