Re: [PATCH v10 1/2] dt-bindings: pinctrl: mt8195: add rsel define

[zhiyong.tao <zhiyong.tao@mediatek.com>]

On Tue, 2021-08-17 at 13:44 +0800, Chen-Yu Tsai wrote:
> On Tue, Aug 17, 2021 at 10:21 AM zhiyong.tao <
> zhiyong.tao@mediatek.com> wrote:
> > 
> > On Tue, 2021-08-17 at 01:00 +0200, Linus Walleij wrote:
> > > On Mon, Aug 16, 2021 at 5:38 PM Chen-Yu Tsai <wenst@chromium.org>
> > > wrote:
> > > > On Mon, Aug 16, 2021 at 6:48 PM zhiyong.tao <
> > > > zhiyong.tao@mediatek.com> wrote:
> > > > > > I'll take that as "use SI units whenever possible and
> > > > > > reasonable".
> > > > > 
> > > > > ==> so It doesn't need to change the define, is it right?
> > > > > we will keep the common define.
> > > > 
> > > > Actually I think it would be possible and reasonable to use SI
> > > > units
> > > > in this case, since you are the vendor and have the resistor
> > > > values
> > > > to implement the support. Having different sets of values for
> > > > different
> > > > chips is nothing out of the ordinary. We already have to
> > > > account
> > > > for
> > > > different number of pins and different pin functions. That is
> > > > what
> > > > compatible strings are for.
> > > 
> > > I fully agree with Chen-Yu's analysis here.
> > > 
> > > Zhiyong can you make an attempt to use SI units (Ohms) and see
> > > what it will look like? I think it will look better for users and
> > > it
> > > will
> > > be less risk to make mistakes.
> > > 
> > > Yours,
> > > Linus Walleij
> > 
> > Hi Linus & chen-yu,
> > 
> > The rsel actual bias resistance of each setting is different in
> > different IC. For example, in mt8195, the rsel actual bias
> > resistance
> > setting like as:
> > MTK_PULL_SET_RSEL_000:75K in PU, 75k in PD;
> > MTK_PULL_SET
> > _RSEL_001:10k in PU, 5k in PD;
> > MTK_PULL_SET_RSEL_010:5k in PU, 75k in
> > PD;
> > MTK_PULL_SET_RSEL_011:4k in PU, 5K in PD;
> > MTK_PULL_SET_RSEL_100:3k in
> > PU, 75k in PD;
> > MTK_PULL_SET_RSEL_101:2k in PU, 5K in PD;
> > MTK_PULL_SET_RSE
> > L_110:1.5k in PU, 75k in PD;
> > MTK_PULL_SET_RSEL_111:1k in PU, 5k in PD.
> > 
> > but in mt8192, the rsel actual bias resistance setting like as:
> > MTK_PULL_SET_RSEL_000:75K in PU, 75k in PD;
> > MTK_PULL_SET_RSEL_001:3k in PU, 5k in PD;
> > MTK_PULL_SET_RSEL_010:10k in PU, 75k in PD;
> > MTK_PULL_SET_RSEL_011:1k in PU, 5K in PD;
> > 
> > Can you help me to provide a suggestion common define for the all
> > different IC?
> > It seems that we should add a new define, if we upstream a new IC
> > pinctrl driver in the future.
> 
> I assume you mean the macros used in the device tree?
> 
> The point of using SI units is to get rid of the macros. Instead of:
> 
>     bias-pull-up = <MTK_PULL_SET_RSEL_000>;
> 
> and
> 
>     bias-pull-down = <MTK_PULL_SET_RSEL_011>;
> 
> We want:
> 
>     bias-pull-up = <75000>;
> 
> and
> 
>     bias-pull-down = <5000>;
> 
> And the pinctrl driver then converts the real values in the device
> tree
> into register values using some lookup table.
> 
> The DT schema could then enumerate all the valid resistor values,
> and get proper validity checking.
> 
> Now if you really wanted to keep some symbols for mapping hardware
> register values to resistor values, you could have
> 
>     #define MT8192_PULL_UP_RSEL_001      75000
>     #define MT8192_PULL_DOWN_RSEL_001     5000
> 
> or have them all named MTK_PULL_{UP,DOWN}_RSEL_NNN, but split into
> different header files, one per SoC.
> 
> Personally I think having the macros is a bad idea if proper values
> are available. It just adds another layer of indirection, and another
> area where errors can creep in.
> 
> 
> Regards
> ChenYu

Hi Chenyu,

In one chip, If GPIO is different, the MTXXXX_PULL_UP_RSEL_001 may
means different actual bias resistance setting.

For example,

KPROW IO                                        
Paramters       Descriptions                   Min      Typ     Max    
 UNIT
Rpd     Input pull-down resistance      40      75      190     Kohm
Rpu     Input pull-up resistance        40      75      190     Kohm
Rpd     Input pull-down resistance      0.8     1.6     2       Kohm
Rpu     Input pull-up resistance        0.8     1.6     2       Kohm
                                        
                                        
KPCOL IO                                        
Paramters       Descriptions                   Min      Typ     Max    
 UNIT
Rpd     Input pull-down resistance      40      75      190     Kohm
Rpu     Input pull-up resistance        40      75      190     Kohm
Rpd     Input pull-down resistance      200     260     400     Kohm
Rpu     Input pull-up resistance        200     260     400     Kohm
                                        
                                        
MSDC1 IO                                        
Paramters       Descriptions                    Min     Typ     Max    
 UNIT
Rpd     Input pull-down resistance      5       7.5     10      Kohm
Rpu     Input pull-up resistance        5       7.5     10      Kohm
Rpd     Input pull-down resistance      10      50      100     Kohm
Rpu     Input pull-up resistance        10      50      100     Kohm

we think that we can't define like this.

Thanks.
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