Hi Uwe,
On Wed, 5 Feb 2025 12:38:32 +0100
Uwe Kleine-König <ukleinek@xxxxxxxxxx> wrote:
> Hello,
>
> I really like this mechanism. Assuming the dt guys are happy yet, I
> intend to merge it. Just some detail question below.
>
> On Wed, Feb 05, 2025 at 10:55:43AM +0100, Herve Codina wrote:
> > Nexus node support in PWM allows the following description:
> > soc {
> > soc_pwm1: pwm-controller1 {
> > #pwm-cells = <3>;
> > };
> >
> > soc_pwm2: pwm-controller2 {
> > #pwm-cells = <3>;
> > };
> > };
> >
> > connector: connector {
> > #pwm-cells = <3>;
> > pwm-map = <0 0 0 &soc_pwm1 1 0 0>,
> > <1 0 0 &soc_pwm2 4 0 0>,
> > <2 0 0 &soc_pwm1 3 0 0>;
> > pwm-map-mask = <0xffffffff 0x0 0x0>;
> > pwm-map-pass-thru = <0x0 0xffffffff 0xffffffff>;
> > };
> >
> > expansion_device {
> > pwms = <&connector 1 57000 0>;
> > };
>
> Does this also work if &soc_pwm2 has #pwm-cells = <2>? Would I need just
>
> pwm-map = <0 0 0 &soc_pwm1 1 0 0>,
> <1 0 0 &soc_pwm2 4 0>,
> <2 0 0 &soc_pwm1 3 0 0>;
Yes, exactly.
>
> then and
>
> pwms = <&connector 1 57000 0>;
>
> would then have the same effect as
>
> pwms = <&soc_pwm2 4 57000>
Yes, the last 0 (or any other values) in pwms = <&connector 1 57000 0> is
simply dropped in the translation (#pwm-cells = 3 in connector nexus to
#pwm-cells = 2 in soc_pwm1 node).
In more generic terms, it works in translation from #pwm-cells = N to
#pwm-cells = M by simply dropping the last N-M values.
Also note that even if values are dropped, you need to have them set when
you point the nexus node because #pwm-cells = 3 is set in the connector
node and need to be fixed and usable for all the entries in the
pwm-map table.
>
> and the 0 is dropped then? Could I adapt the mapping that the effect is
>
> pwms = <&soc_pwm2 57000 0>
In this one, I think you miss the PWM number
If I read correctly this line you ask for the PWM 57000 from the soc_pwm2
controller. This doesn't make sense :)
If I didn't answer already, can you clarify your point here ?
>
> instead?
>
> This smells a bit ugly and I wonder if this gives a motivation to extend
> the binding for PWMs that use #pwm-cells = <2> (or less) to also accept
> the default 3-cell binding.
With my understanding in the translation performed, this is not needed.
Also the following translation works:
soc {
soc_pwm1: pwm-controller1 {
#pwm-cells = <2>;
};
soc_pwm2: pwm-controller2 {
#pwm-cells = <3>;
};
};
connector: connector {
#pwm-cells = <2>; <--------- Note the 2 here
pwm-map = <0 0 &soc_pwm1 1 0>,
<1 0 &soc_pwm2 4 0 123>,
pwm-map-mask = <0xffffffff 0x0>; <---- #pwm-cells = <2>
pwm-map-pass-thru = <0x0 0xffffffff>; <---- #pwm-cells = <2>
};
pwms = <&connector 1 57000> translates to pwms = <&soc_pwm2 1 57000 123>
The last value in the translation (i.e 123) was added during the translation
(#pwm-cells = <2> to #pwm-cells = <3>) from the value set in the pwm-map
table.
Hope I answered your questions.
Best regards,
Hervé
