Re: [RFC PATCH v3 3/5] platform/chrome: Introduce device tree hardware prober - Chen-Yu Tsai

From: Chen-Yu Tsai <wenst@chromium.org>
To: Doug Anderson <dianders@chromium.org>
Cc: Rob Herring <robh+dt@kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	 Matthias Brugger <matthias.bgg@gmail.com>,
	 AngeloGioacchino Del Regno
	<angelogioacchino.delregno@collabora.com>,
	Wolfram Sang <wsa@kernel.org>,
	 Benson Leung <bleung@chromium.org>,
	Tzung-Bi Shih <tzungbi@kernel.org>,
	 chrome-platform@lists.linux.dev, devicetree@vger.kernel.org,
	 linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org,
	 linux-kernel@vger.kernel.org, Johan Hovold <johan@kernel.org>,
	 Hsin-Yi Wang <hsinyi@chromium.org>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	 andriy.shevchenko@linux.intel.com,
	Jiri Kosina <jikos@kernel.org>,
	 linus.walleij@linaro.org, broonie@kernel.org,
	gregkh@linuxfoundation.org,  hdegoede@redhat.com,
	james.clark@arm.com, james@equiv.tech,  keescook@chromium.org,
	rafael@kernel.org, tglx@linutronix.de,
	 Jeff LaBundy <jeff@labundy.com>,
	linux-input@vger.kernel.org, linux-i2c@vger.kernel.org
Subject: Re: [RFC PATCH v3 3/5] platform/chrome: Introduce device tree hardware prober
Date: Mon, 4 Dec 2023 15:24:42 +0800	[thread overview]
Message-ID: <CAGXv+5Hz3wfjCRa2AiOQgOv7zo8bzAmtG=a=jWJhO2MZNrFtpw@mail.gmail.com> (raw)
In-Reply-To: <CAD=FV=XV0+G=uFBE_n6WFGVW2szGcKToZgCNTdSrNf3LVk9MOQ@mail.gmail.com>

On Sat, Dec 2, 2023 at 8:58 AM Doug Anderson <dianders@chromium.org> wrote:
>
> Hi,
>
> On Tue, Nov 28, 2023 at 12:45 AM Chen-Yu Tsai <wenst@chromium.org> wrote:
> >
> > @@ -61,6 +61,17 @@ config CHROMEOS_TBMC
> >           To compile this driver as a module, choose M here: the
> >           module will be called chromeos_tbmc.
> >
> > +config CHROMEOS_OF_HW_PROBER
> > +       bool "ChromeOS Device Tree Hardware Prober"
>
> Any reason that it can't be a module?

No technical one. However if it's a module, the user has to manually load
it. So I think it's more of a usability thing.

OOTH I think this needs to be a module if I2C is built as a module.
Somehow I had thought of it at one point but then it slipped my mind.

> > +       depends on OF
> > +       depends on I2C
> > +       select OF_DYNAMIC
> > +       default OF
>
> You probably don't want "default OF". This means that everyone will
> automatically get this new driver enabled which is unlikely to be
> right.

I thought this whole section was guarded behind KCONFIG_CHROME_PLATFORMS.
So if the user has CHROME_PLATFORMS enabled and has OF enabled, they
likely need the prober.

> > +static int chromeos_of_hw_prober_probe(struct platform_device *pdev)
> > +{
> > +       for (size_t i = 0; i < ARRAY_SIZE(hw_prober_platforms); i++)
> > +               if (of_machine_is_compatible(hw_prober_platforms[i].compatible)) {
> > +                       int ret;
> > +
> > +                       ret = hw_prober_platforms[i].prober(&pdev->dev,
> > +                                                           hw_prober_platforms[i].data);
> > +                       if (ret)
>
> Should it only check for -EPROBE_DEFER here? ...and then maybe warn
> for other cases and go through the loop? If there's some error
> enabling the touchscreen I'd still want the trackpad to probe...

Makes sense. However there's no extra information to give in the
warning though.

> > +                               return ret;
> > +               }
> > +
> > +       return 0;
>
> Random thought: once we get here, the driver is useless / just wasting
> memory. Any way to have it freed? ;-)

I don't think there is a good way to do that, except maybe marking all
the functions as __init? But that likely doesn't work in combination
with deferred probing (say the i2c driver is a module).

ChenYu