PWM...

[Arnd Bergmann]

On Sunday 19 January 2014 11:03:24 Olof Johansson wrote:
> > 
> > Yes, because iMX6 specifies #pwm-cells as 2, there's no flags able to
> > be specified in the pwms declaration in pwmleds.  So that doesn't work.
> > There's no property to tell pwmleds that it should use inverted sense
> > either.
> 
> Adding a property for active-low to the pwm-leds binding would be
> easy, and backwards compatible. I'm surprised the original binding
> didn't specify it. The leds-pwm driver already seems to support it for
> C-configured instances.
> 
> I'm also surprised that the imx pwm driver even has a #pwm-cells of
> two, since the driver only supports one output. It'd be nice if they
> had allocated the extra cell for flags, but it's hard to change now,
> unless you do a new binding/compatible value and deprecate the old one.

Actually I think it's not that hard to change: The binding can specify
that either #pwm-cells=<2> or #pwm-cells=<3> is supported, and the
driver extended to handle both cases. This would maintain backwards
compatibility for old dtb files, though no forward compatibility for
new dtb files with old kernels.

	Arnd