linux-kernel - Re: [PATCH v9 7/7] arm64: dts: mediatek: mt8173-elm-hana: Mark touchscreens and trackpads as fail

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Message-ID: <CAD=FV=VbTMLr8ybCvKwm4aau+UkwCewuj2mqFX_+9hdCALLBRA@mail.gmail.com>
Date: Mon, 28 Oct 2024 08:42:51 -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>, 
	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 v9 7/7] arm64: dts: mediatek: mt8173-elm-hana: Mark
 touchscreens and trackpads as fail

Hi,

On Mon, Oct 28, 2024 at 2:14 AM Chen-Yu Tsai <wenst@...omium.org> wrote:
>
> > > @@ -35,6 +37,7 @@ touchscreen@40 {
> > >                 hid-descr-addr = <0x0001>;
> > >                 interrupt-parent = <&pio>;
> > >                 interrupts = <88 IRQ_TYPE_LEVEL_LOW>;
> > > +               status = "fail-needs-probe";
> >
> > It's a little weird that there's no pinctrl definition for the
> > touchscreens but there is one for the trackpad, but that predates your
> > patch and is unlikely to be a big deal.
>
> To be honest I'm in favor of getting rid of pinctrl settings that
> do nothing more than mux in a GPIO, as mentioned in my talk at ELCE.
> Such settings are already implied by the interrupts or gpios properties.
> The fact that the OS doesn't enforce exclusiveness between the
> subsystems is not something the DT should deal with.

One could also argue that the fact that the Linux kernel happens to
auto-mux pins to GPIO is not something that the device tree should
assume. Personally I have never liked the "auto-mux" behavior of Linux
and I've found that it can get in the way when you need to do more
advanced pinmuxing, like when a driver needs to sometimes use a pin in
"special function" mode and sometimes in GPIO mode. The auto-muxing
happens behind the back of the driver which then needs to account for
this fact and work around it. Just sayin. :-P