linux-kernel - Re: [PATCH 8/9] arm64: dts: mediatek: mt8183-kukui: Fix pull-down/up-adv values

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Message-ID: <CAGXv+5FXZ_byK8Ftb9LjfQMkgtLd7mTmWgz_Nsvcv8=jy53T=g@mail.gmail.com>
Date: Tue, 19 Aug 2025 13:29:44 +0800
From: Chen-Yu Tsai <wenst@...omium.org>
To: Linus Walleij <linus.walleij@...aro.org>
Cc: Julien Massot <julien.massot@...labora.com>, kernel@...labora.com, 
	Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Ikjoon Jang <ikjn@...omium.org>, 
	Enric Balletbo i Serra <eballetbo@...nel.org>, Weiyi Lu <weiyi.lu@...iatek.com>, 
	Eugen Hristev <eugen.hristev@...aro.org>, Liam Girdwood <lgirdwood@...il.com>, 
	Mark Brown <broonie@...nel.org>, Julien Massot <jmassot@...labora.com>, 
	Sean Wang <sean.wang@...nel.org>, linux-clk@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org, 
	linux-sound@...r.kernel.org, linux-gpio@...r.kernel.org
Subject: Re: [PATCH 8/9] arm64: dts: mediatek: mt8183-kukui: Fix
 pull-down/up-adv values

On Tue, Aug 19, 2025 at 1:27 PM Chen-Yu Tsai <wenst@...omium.org> wrote:
>
> On Mon, Aug 18, 2025 at 11:22 PM Linus Walleij <linus.walleij@...aro.org> wrote:
> >
> > On Wed, Aug 6, 2025 at 8:38 AM Chen-Yu Tsai <wenst@...omium.org> wrote:
> > > On Fri, Aug 1, 2025 at 7:18 PM Julien Massot wrote
> >
> > > >                 pins-clk {
> > > >                         pinmux = <PINMUX_GPIO124__FUNC_MSDC0_CLK>;
> > > >                         drive-strength = <MTK_DRIVE_14mA>;
> > > > -                       mediatek,pull-down-adv = <10>;
> > > > +                       mediatek,pull-down-adv = <2>;
> > >
> > >         bias-pull-down = <MTK_PUPD_SET_R1R0_10>;
> > >
> > > and so on.
> > >
> > > ChenYu
> >
> > I agree with ChenYu, the more standardized properties are the better it is.
> >
> > All the custom properties makes sense for an engineer working with just
> > that one SoC (like the SoC vendor...) but for field engineers who have
> > to use different SoCs every day this is just a big mess for the mind.
> >
> > The standard properties are clear, concise and tell you exactly what
> > they are about.
> >
> > The argument should be in Ohms though, according to the standard
> > bindings, but maybe the value of MTK_PUPD_SET_R1R0_10 is
> > something like that?
>
> For reasons I can't recall clearly these are just placeholder values
> that the driver then maps to the R1 and R0 settings. But at least they
> use the standard properties.
>
> The reason was either one of the following or both:
>
>   a. not every group of pins had the same resistance values for R1 & R0
>   b. there are no known precise values; the values depend on the process
>      and batch

Also, their customers seemed more accustomed to dealing with toggling
R1 & R0 vs setting some actual value. I presume that comes with the
uncertainty of the actual hardware value, and they just try which
combination works better.

ChenYu