RE: [PATCH v11 1/4] dt-bindings: pinctrl: mt8195: add rsel define

["Light Hsieh (謝明燈)" <Light.Hsieh@mediatek.com>]

For backward compatible to previous usage and many customers of mediatek, MTK would not change previous usage of bias-pull-up and bias-pull-down setting usage.

The si unit usage will only apply to rsel only.

Please sto  give comments on changing mediatek's previous usage.

Light

-----Original Message-----
From: Chen-Yu Tsai [mailto:wenst@chromium.org] 
Sent: Wednesday, September 15, 2021 11:25 AM
To: Zhiyong Tao (陶志勇)
Cc: Rob Herring; Linus Walleij; Mark Rutland; Matthias Brugger; Sean Wang; srv_heupstream; Hui Liu (刘辉); Eddie Huang (黃智傑); Light Hsieh (謝明燈); Biao Huang (黄彪); Hongzhou Yang; Sean Wang; Seiya Wang (王迺君); Devicetree List; LKML; moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE; moderated list:ARM/Mediatek SoC support; open list:GPIO SUBSYSTEM
Subject: Re: [PATCH v11 1/4] dt-bindings: pinctrl: mt8195: add rsel define

On Tue, Sep 14, 2021 at 8:27 PM zhiyong.tao <zhiyong.tao@mediatek.com> wrote:
>
> On Mon, 2021-09-06 at 16:20 +0800, Chen-Yu Tsai wrote:
> > On Sat, Sep 4, 2021 at 4:40 PM zhiyong.tao 
> > <zhiyong.tao@mediatek.com>
> > wrote:
> > >
> > > On Thu, 2021-09-02 at 11:35 +0800, Chen-Yu Tsai wrote:
> > > > On Thu, Sep 2, 2021 at 10:54 AM zhiyong.tao < 
> > > > zhiyong.tao@mediatek.com
> > > > > wrote:
> > > > >
> > > > > On Wed, 2021-09-01 at 12:35 +0800, Chen-Yu Tsai wrote:
> > > > > > On Mon, Aug 30, 2021 at 8:36 AM Zhiyong Tao < 
> > > > > > zhiyong.tao@mediatek.com> wrote:
> > > > > > >
> > > > > > > This patch adds rsel define for mt8195.
> > > > > > >
> > > > > > > Signed-off-by: Zhiyong Tao <zhiyong.tao@mediatek.com>
> > > > > > > ---
> > > > > > >  include/dt-bindings/pinctrl/mt65xx.h | 9 +++++++++
> > > > > > >  1 file changed, 9 insertions(+)
> > > > > > >
> > > > > > > diff --git a/include/dt-bindings/pinctrl/mt65xx.h
> > > > > > > b/include/dt-
> > > > > > > bindings/pinctrl/mt65xx.h
> > > > > > > index 7e16e58fe1f7..f5934abcd1bd 100644
> > > > > > > --- a/include/dt-bindings/pinctrl/mt65xx.h
> > > > > > > +++ b/include/dt-bindings/pinctrl/mt65xx.h
> > > > > > > @@ -16,6 +16,15 @@
> > > > > > >  #define MTK_PUPD_SET_R1R0_10 102  #define 
> > > > > > > MTK_PUPD_SET_R1R0_11 103
> > > > > > >
> > > > > > > +#define MTK_PULL_SET_RSEL_000  200 #define 
> > > > > > > +MTK_PULL_SET_RSEL_001  201 #define MTK_PULL_SET_RSEL_010  
> > > > > > > +202 #define MTK_PULL_SET_RSEL_011  203 #define 
> > > > > > > +MTK_PULL_SET_RSEL_100  204 #define MTK_PULL_SET_RSEL_101  
> > > > > > > +205 #define MTK_PULL_SET_RSEL_110  206 #define 
> > > > > > > +MTK_PULL_SET_RSEL_111  207
> > > > > >
> > > > > > Could you keep the spacing between constants tighter, or 
> > > > > > have no spacing at all? Like having MTK_PULL_SET_RSEL_000 
> > > > > > defined as 104 and so on. This would reduce the chance of 
> > > > > > new macro values colliding with actual resistor values set 
> > > > > > in the datasheets, plus a contiguous space would be easy to 
> > > > > > rule as macros.
> > > > > >
> > > > > > ChenYu
> > > > >
> > > > > Hi chenyu,
> > > > > By the current solution, it won't be mixed used by 
> > > > > MTK_PULL_SET_RSEL_XXX and real  resistor value.
> > > > > If user use MTK_PULL_SET_RSEL_XXX, They don't care the define 
> > > > > which means how much resistor value.
> > > >
> > > > What I meant was that by keeping the value space tight, we avoid 
> > > > the situation where in some new chip, one of the RSEL resistors 
> > > > happens to be 200 or 300 ohms. 100 is already taken, so there's 
> > > > nothing we can do if new designs actually do have 100 ohm 
> > > > settings.
> > > >
> > > > > We think that we don't contiguous macro space for different 
> > > > > register.
> > > > > It may increase code complexity to make having
> > > > > MTK_PULL_SET_RSEL_000
> > > > > defined as 104.
> > > >
> > > > Can you elaborate? It is a simple range check and offset 
> > > > handling.
> > > > Are
> > > > you concerned that a new design would have R2R1R0 and you would 
> > > > like the macros to be contiguous?
> > > >
> > > > BTW I don't quite get why decimal base values (100, 200, etc.) 
> > > > were chosen. One would think that binary bases are easier to 
> > > > handle in code.
> > > >
> > > >
> > > > ChenYu
> > > >
> > >
> > > Yes,we concerned that a new design would have R2R1R0 and we would 
> > > like the macros to be contiguous in the feature. we reserve it.
> >
> > I see. That makes sense. Do you expect to see R3 or even R4 in the 
> > future?
> > Or put another way, do you expect to see resistor values of 150 or
> > 200
> > supported?
> >
> > Maybe we could reserve 200 and start from 201 for the RSEL macros?
> >
> > Some planning needs to be done here to avoid value clashes.
> >
> > > We think that decimal and binary base values are the same for the 
> > > feature.
> >
> > With decimal numbers you end up wasting a bit more space, since the 
> > hardware is always using binary values. I just found it odd, that's 
> > all.
> >
> > ChenYu
> >
> > > > > Thanks.
>
> Hi ChenYu,
>
> In the next version, we provide a solution which we discussed internal 
> to avoid value clashes.
>
> The solution:
> 1. We will keep the define "MTK_PULL_SET_RSEL_000 200". It won't 
> change.
>
> 2. We will add a property in pio dtsi node, for example, the property 
> name is "rsel_resistance_in_si_unit".
> We will add a flag "rsel_si_unit" in pinctrl device.
> in probe function, we will identify the property name 
> "rsel_resistance_in_si_unit" to set the flag "rsel_si_unit" value.
> So it can void value clashes.

I suppose a "mediatek," prefix should be added. And to future proof things this should probably apply to all bias-up/down values, so "mediatek,bias-resistance-in-si-units"?

And the description should include something like that:

  Past usage of bias-up/down values included magic numbers to specify
  different hardware configurations based on register values. This
  property specifies that all values used for bias-up/down for this
  controller shall be in SI units.

And this proposal is still subject to maintainer (not me) review.


> 3.We will provide the define "MTK_PULL_SET_RSEL_000 200" and si unit 
> two solution. users can support which solution by add property 
> "rsel_resistance_in_si_unit" in dts node or not.

Thanks. I think this solution does provide a clear separation of the two value spaces.

ChenYu

> > > > >
> > > > > >
> > > > > > >  #define MTK_DRIVE_2mA  2
> > > > > > >  #define MTK_DRIVE_4mA  4
> > > > > > >  #define MTK_DRIVE_6mA  6
> > > > > > > --
> > > > > > > 2.18.0
> > > > > > > _______________________________________________
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