Hello Andy, On Mon, Jun 07, 2021 at 02:49:01PM +0300, Andy Shevchenko wrote: > On Mon, Jun 07, 2021 at 01:21:01PM +0300, Andy Shevchenko wrote: > > On Mon, Jun 07, 2021 at 01:15:20PM +0300, Andy Shevchenko wrote: > > > 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 > > > > Hmm... I have read the actual implementation and it seems it's possible to have > > flexible array, so this patch needs to be reconsidered. > > I was thinking more about it and what we have here is positional-dependent > arguments. Either way we might end up in the same situation (when we need to > parse arguments based on their positions, rather than always have them being > present). So, while I won't change documentation example (to be more stricter > there), I will drop this change. > > Also, the PWM initial state doesn't include duty cycle. Any explanations why is > that? This isn't technically the initial state. It's a hint to the consumer which period to pick. The duty-cycle is usually variable, but if I designed the binding today I would not include the period in the pwm handle. But to discuss this is moot---the binding is as it is. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ |
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