Hi Uwe, On Wed, 5 Feb 2025 17:29:30 +0100 Uwe Kleine-König <ukleinek@xxxxxxxxxx> wrote: > Hello Hervé, > > On Wed, Feb 05, 2025 at 02:37:37PM +0100, Herve Codina wrote: > > On Wed, 5 Feb 2025 12:38:32 +0100 > > Uwe Kleine-König <ukleinek@xxxxxxxxxx> wrote: > > > 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. > > Makes sense. > > > > 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 :) > > Some pwm chip devices with only a single output line use this. The first > paramter is the default period (which is passed in the 2nd parameter > normally) and the 2nd paramter are flags (normally the 3rd parameter). > Back then the rationale was that for such hardware, the line index is > zero always anyhow, and so could better be skipped. > > Compare of_pwm_xlate_with_flags() to of_pwm_single_xlate(). pwm-pxa is > the single offender using the latter. Thinking about that, it's easy > enough to fix without breaking compatibility. I'll tackle that. > > So for a PWM on pxa `<&soc_pwm2 57000 0>` works fine. I see. In this case, a parameter shift during translation would be needed to skip the PWM line index in the translated arguments. This is not currently neither described in device-tree specicication [0] nor handled in the common code of_parse_phandle_with_args_map() in the kernel. This use case can appear for resources other than PWMs and IMHO it should be nice to have it supported. I think this support should proposed out of this series adding support for PWM nexus nodes. Is it blocking for this current series ? [0] https://github.com/devicetree-org/devicetree-specification/releases/download/v0.4/devicetree-specification-v0.4.pdf Best regards, Hervé
