On Tue, Oct 07, 2014 at 03:55:33PM +0200, Lothar Waßmann wrote:
> Change the pwm chip driver registration, so that a chip driver that
> supports polarity inversion can still be used with DTBs that don't
> provide the 'PWM_POLARITY' flag.
> 
> This is done to provide polarity inversion support for the pwm-imx
> driver without having to modify all existing DTS files.

I don't like how this throws out the window the only sanity checking we
have in place for the #pwm-cells property.

As I understand it, the problem that you're trying to solve is one of
backwards-compatibility where existing device trees have #pwm-cells =
<2>, but the driver is extended to support flags as well.

In that case, can we not simply make of_pwm_xlate_with_flags() support
that case transparently? That is, if the driver sets .of_pwm_n_cells to
3, we can still support #pwm-cells = <2> and use the default (no) flags
instead.

Something like the below should do that (compile-tested only).

Thierry