On 11.04.2017 11:50, Boris Brezillon wrote: > On Tue, 11 Apr 2017 11:33:44 +0300 > m18063 <claudiu.bez...@microchip.com> wrote: > >> On 10.04.2017 19:27, Boris Brezillon wrote: >>> On Mon, 10 Apr 2017 18:01:37 +0200 >>> Boris Brezillon <boris.brezil...@free-electrons.com> wrote: >>> >>>> On Mon, 10 Apr 2017 17:10:11 +0200 >>>> Thierry Reding <thierry.red...@gmail.com> 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 <claudiu.bez...@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.bez...@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. >>>> >>>> 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. >>> >>> Note that we need drivers to implement both ->apply() and ->get_state() >>> for this approach to work correctly, and we also need some help from >>> the core to reset the PWM states at resume time, otherwise >>> pwm_apply_state() will just compare the old state to the new one, see >>> that they match and never call the ->apply() method. >>> >>> Another solution would be to remove the memcmp here [1] and >>> unconditionally call ->apply(). >> There are drivers which checks, in ->apply() hooks, the current PWM state >> before applying the new state or take actions based on differences >> b/w current and new PWM states. Removing memcmp without resetting >> the PWM state would lead to wrong states in those drivers. > > Indeed. So it just leaves the solution where we implement ->get_state(). > Honestly, it shouldn't be too hard to do that in the atmel driver. I agree. > > Note that for drivers that do not implement ->get_state(), the first > pwm_apply_state() after the system has resumed should be harmless, > because the current PWM should exactly match the one the PWM user is > re-applying. I agree.
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