Re: [PATCH] backlight: pwm_bl: configure pwm only once per backlight toggle

[Daniel Thompson <daniel.thompson@linaro.org>]

On Thu, Oct 17, 2019 at 02:19:45PM +0200, Uwe Kleine-König wrote:
> On Thu, Oct 17, 2019 at 12:47:27PM +0100, Daniel Thompson wrote:
> > On Thu, Oct 17, 2019 at 10:10:59AM +0200, Uwe Kleine-König wrote:
> > > A previous change in the pwm core (namely 01ccf903edd6 ("pwm: Let
> > > pwm_get_state() return the last implemented state")) changed the
> > > semantic of pwm_get_state() and disclosed an (as it seems) common
> > > problem in lowlevel PWM drivers. By not relying on the period and duty
> > > cycle being retrievable from a disabled PWM this type of problem is
> > > worked around.
> > > 
> > > Apart from this issue only calling the pwm_get_state/pwm_apply_state
> > > combo once is also more effective.
> > 
> > I'm only interested in the second paragraph here.
> > 
> > There seems to be a reasonable consensus that the i.MX27 and cros-ec
> > PWM drivers should be fixed for the benefit of other PWM clients.
> > So we make this change because it makes the pwm-bl better... not to
> > work around bugs ;-).
> 
> That's fine, still I think it's fair to explain the motivation of
> creating this patch.

Maybe.

Whether this patch is a workaround or simply an improvement to pwm-bl
does need to be clear since it affects whether Lee steers it towards
v5.4-rcX or linux-next .


Daniel.