On Mon, Jun 07, 2021 at 11:53:24AM +0200, Uwe Kleine-König wrote: > On Mon, Jun 07, 2021 at 12:02:37PM +0300, Andy Shevchenko wrote: > > On Sun, Jun 06, 2021 at 11:30:54PM +0200, Uwe Kleine-König wrote: > > > On Mon, May 31, 2021 at 10:49:42PM +0300, Andy Shevchenko wrote: > > > > It makes little sense to make PWM flags optional since in case > > > > of multi-channel consumer the flags can be optional only for > > > > the last listed channel. > > > > > > I think the same holds true for dt references. > > > > Can you elaborate this? I haven't got what you are talking about, not a DT > > expert here. > > Ah no, I mixed that up. While the function that parses the phandle is > flexible, for each pwm controller the number of arguments is fixed, so > > pwms = <&pwm1 100000 &pwm2 100000 &pwm3 1000000>; > > cannot be interpreted as 3-argument references to two PWMs. This is > different to ACPI (I guess, not an ACPI expert here :-) because &pwm1 > "knows" if it needs 1 or 2 additional parameters (#pwm-cells). It's not about ACPI, it's about "the ACPI glue layer in Linux kernel". Used API is a part of it and it does allow only two cases, either NULL entry (by having 0 as an argument) or full-length supplied tuple (in case of PWM it's 3, so, means 4 parameters. Let's consider examples: (0, 0, x3, y3, z3, t3) // NULL, NULL, PWM3 (x1, y1, z1, t1, 0, x3, y3, z3, t3) // PWM1, NULL, PWM3 So, making last parameter "flexible" will work only for the last tuple in the array. Read this [1] for further information. [1]: https://elixir.bootlin.com/linux/latest/source/drivers/acpi/property.c#L629 -- With Best Regards, Andy Shevchenko
