Messages in this thread | | | Date | Mon, 10 Apr 2017 17:10:11 +0200 | From | Thierry Reding <> | Subject | Re: [PATCH] drivers: pwm: pwm-atmel: implement suspend/resume functions |
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On Mon, Apr 10, 2017 at 04:35:58PM +0200, Boris Brezillon wrote: > On Mon, 10 Apr 2017 17:20:20 +0300 > Claudiu Beznea <claudiu.beznea@microchip.com> wrote: > > > Implement suspend and resume power management specific > > function to allow PWM controller to correctly suspend > > and resume. > > > > Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com> > > --- > > 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.
Any thoughts on that?
Thierry [unhandled content-type:application/pgp-signature] | |