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

[Julien Massot <julien.massot@collabora.com>]

Hi,
On Tue, 2025-08-19 at 13:29 +0800, Chen-Yu Tsai wrote:
> On Tue, Aug 19, 2025 at 1:27 PM Chen-Yu Tsai <wenst@chromium.org> wrote:
> > 
> > On Mon, Aug 18, 2025 at 11:22 PM Linus Walleij <linus.walleij@linaro.org> wrote:
> > > 
> > > On Wed, Aug 6, 2025 at 8:38 AM Chen-Yu Tsai <wenst@chromium.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
> 
> I don't know for (b), but no there is a lot of different values for R1 & R0
> 

From what I saw in the register table
We can have for the pull up resistors
75K / 200K
2K  / 75K
5K  / 20K
50k / 10K 

And for the pull down ones:

75k/2k
75k/75k
10k/50k

And we can have a combination of both resistors that will give odd values 
(e.g 1948 Ohm for 2k/75K, 545454 Ohm for 75k/200k) to express in the device tree 


> 
> 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

Regards,
Julien