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

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:

quoted

On Tue, 2021-08-17 at 01:00 +0200, Linus Walleij wrote:

quoted

On Mon, Aug 16, 2021 at 5:38 PM Chen-Yu Tsai [off-list ref]
wrote:

quoted

On Mon, Aug 16, 2021 at 6:48 PM zhiyong.tao <
zhiyong.tao@mediatek.com> wrote:

quoted

quoted

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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