On Mon, 10 Apr 2017 17:10:11 +0200 Thierry Reding <[email protected]> wrote:
> On Mon, Apr 10, 2017 at 04:35:58PM +0200, Boris Brezillon wrote: > > On Mon, 10 Apr 2017 17:20:20 +0300 > > Claudiu Beznea <[email protected]> wrote: > > > > > Implement suspend and resume power management specific > > > function to allow PWM controller to correctly suspend > > > and resume. > > > > > > Signed-off-by: Claudiu Beznea <[email protected]> > > > --- > > > drivers/pwm/pwm-atmel.c | 81 > > > +++++++++++++++++++++++++++++++++++++++++++++++++ > > > 1 file changed, 81 insertions(+) > > > > > > diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c > > > index 530d7dc..75177c6 100644 > > > --- a/drivers/pwm/pwm-atmel.c > > > +++ b/drivers/pwm/pwm-atmel.c > > > @@ -58,6 +58,8 @@ > > > #define PWM_MAX_PRD 0xFFFF > > > #define PRD_MAX_PRES 10 > > > > > > +#define PWM_MAX_CH_NUM (4) > > > + > > > struct atmel_pwm_registers { > > > u8 period; > > > u8 period_upd; > > > @@ -65,11 +67,18 @@ struct atmel_pwm_registers { > > > u8 duty_upd; > > > }; > > > > > > +struct atmel_pwm_pm_ctx { > > > + u32 cmr; > > > + u32 cdty; > > > + u32 cprd; > > > +}; > > > + > > > struct atmel_pwm_chip { > > > struct pwm_chip chip; > > > struct clk *clk; > > > void __iomem *base; > > > const struct atmel_pwm_registers *regs; > > > + struct atmel_pwm_pm_ctx ctx[PWM_MAX_CH_NUM]; > > > > Hm, I'm pretty sure you can rely on the current PWM state and call > > atmel_pwm_apply() at resume time instead of doing that. See what I did > > here [1]. > > > > Thierry, maybe it's time to start thinking about a generic solution to > > save/restore PWM states. > > Generally speaking I think applying the states are the right way to go. > Ideally the PWM core could simply resume all of the PWM channels that a > device exports and the ->apply() callback would be enough to restore > that. I'm not sure if that's going to work with current implementations, > though. Your pwm-atmel-hlcdc patch certainly indicates that we're not > quite there yet. > > On the other hand, I'm beginning to think that maybe PWMs are too low- > level for this kind of suspend/resume. For example if you use the PWM to > control a backlight brightness, restoring it via the driver core's > resume hook is potentially going to turn it back on at the wrong time. I > have a feeling that we might be better off just pushing this up to the > PWM users. A slight special case might be sysfs, for which no external > user driver exists. But we already have separate data structures to keep > track of sysfs-related context, so suspend/resume support could be added > there. Yep, you're probably right, we should let the PWM user take care of re-applying the PWM state, because it's the only one having enough knowledge about what the PWM is really driving to take a wise decision. This goes against my patch adding suspend/resume hooks to the pwm-atmel-hlcdc driver, but we can easily drop the call to atmel_hlcdc_pwm_apply() in ->resume() once we have patched the pwm-backlight driver to take care of that.
