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From:   Chen-Yu Tsai <wenst@chromium.org>
Date:   Mon, 4 Dec 2023 15:53:31 +0800
Message-ID: <CAGXv+5HQeXPyRVFXaPKwX6GDoeMVM0Sneqk4CJx1AWGYT-mAEg@mail.gmail.com>
Subject: Re: [RFC PATCH v3 3/5] platform/chrome: Introduce device tree
 hardware prober
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
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On Mon, Dec 4, 2023 at 3:24=E2=80=AFPM Chen-Yu Tsai <wenst@chromium.org> wr=
ote:
>
> On Sat, Dec 2, 2023 at 8:58=E2=80=AFAM Doug Anderson <dianders@chromium.o=
rg> wrote:
> >
> > Hi,
> >
> > On Tue, Nov 28, 2023 at 12:45=E2=80=AFAM Chen-Yu Tsai <wenst@chromium.o=
rg> 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.

We could probably manually add module aliases. I thought about aliases
against the machine compatibles, but there doesn't seem to be a device
for it to trigger. Or target something common to ChromeOS devices like
the EC? It's really hacky though.

ChenYu

> 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 =3D 0; i < ARRAY_SIZE(hw_prober_platforms); i++=
)
> > > +               if (of_machine_is_compatible(hw_prober_platforms[i].c=
ompatible)) {
> > > +                       int ret;
> > > +
> > > +                       ret =3D 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