linux-kernel - Re: [PATCH v8 6/8] i2c: of-prober: Add GPIO support to simple helpers

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Message-ID: <Zw5QKDoZkn6QZtNO@smile.fi.intel.com>
Date: Tue, 15 Oct 2024 14:21:12 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
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>, 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,
	Douglas Anderson <dianders@...omium.org>,
	Johan Hovold <johan@...nel.org>, Jiri Kosina <jikos@...nel.org>,
	linux-i2c@...r.kernel.org
Subject: Re: [PATCH v8 6/8] i2c: of-prober: Add GPIO support to simple helpers

On Tue, Oct 15, 2024 at 01:34:52PM +0800, Chen-Yu Tsai wrote:
> On Mon, Oct 14, 2024 at 7:20 PM Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
> > On Mon, Oct 14, 2024 at 12:06:16PM +0800, Chen-Yu Tsai wrote:
> > > On Thu, Oct 10, 2024 at 11:20 PM Andy Shevchenko
> > > <andriy.shevchenko@...ux.intel.com> wrote:
> > > > On Tue, Oct 08, 2024 at 03:34:25PM +0800, Chen-Yu Tsai wrote:

...

> > > > > +static void i2c_of_probe_simple_disable_gpio(struct device *dev, struct i2c_of_probe_simple_ctx *ctx)
> > > > > +{
> > > > > +     if (!ctx->gpiod)
> > > > > +             return;
> > > >
> > > > Do you need this check for the future patches?
> > >
> > > Not sure I follow. The check is needed because this function is called
> > > in i2c_of_probe_simple_cleanup(), but the GPIO could have been released
> > > earlier in i2c_of_probe_simple_cleanup_early(), and that makes this
> > > function a no-op.
> >
> > Do you have a known race condition then? This is bad. You shouldn't rely on
> > the sequence of events here, or the serialisation has to be added.
> >
> > > The helpers for the release side are quite short, but the ones on the
> > > request side wrap some conditional and error handling. I think it's
> > > better to keep it symmetric?
> >
> > Yes, but why do you need the above check, I didn't still get...
> > I.o.w. you think that there is a gap in time that (if no check) the GPIO
> > descriptor might be changed? But then how does it affect anyway the possibility
> > that it becomes not NULL even with the current code.
> 
> The opposite actually. Either it is always NULL, or it was initially valid,
> but the early cleanup function released it and thus it became NULL by the
> time this function gets called.

Then I don't see any points to have this check (details in the other reply).

> > > > > +     /* Ignore error if GPIO is not in output direction */
> > > > > +     gpiod_set_value(ctx->gpiod, !ctx->opts->gpio_assert_to_enable);
> > > > > +}

-- 
With Best Regards,
Andy Shevchenko