Messages in this thread | | | Subject | Re: [PATCH] pwm: cros-ec: Let cros_ec_pwm_get_state() return the last applied state | From | Enric Balletbo i Serra <> | Date | Wed, 9 Oct 2019 12:19:38 +0200 |
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On 9/10/19 12:16, Uwe Kleine-König wrote: > On Wed, Oct 09, 2019 at 10:56:35AM +0100, Daniel Thompson wrote: >> On Wed, Oct 09, 2019 at 11:27:13AM +0200, Enric Balletbo i Serra wrote: >>> Hi Uwe, >>> >>> Adding Daniel and Lee to the discussion ... >> >> Thanks! >> >>> On 8/10/19 22:31, Uwe Kleine-König wrote: >>>> On Tue, Oct 08, 2019 at 06:33:15PM +0200, Enric Balletbo i Serra wrote: >>>>>> A few thoughts to your approach here ...: >>>>>> >>>>>> - Would it make sense to only store duty_cycle and enabled in the >>>>>> driver struct? >>>>>> >>>>> >>>>> Yes, in fact, my first approach (that I didn't send) was only storing enabled >>>>> and duty cycle. For some reason I ended storing the full pwm_state struct, but I >>>>> guess is not really needed. >>>>> >>>>> >>>>>> - Which driver is the consumer of your pwm? If I understand correctly >>>>>> the following sequence is the bad one: >>>>>> >>>>> >>>>> The consumer is the pwm_bl driver. Actually I'n trying to identify >>>>> other consumers. >>>> >>> >>> So far, the pwm_bl driver is the only consumer of cros-ec-pwm. >>> >>>> Ah, I see why I missed to identify the problem back when I checked this >>>> driver. The problem is not that .duty_cycle isn't set but there .enabled >>>> isn't set. So maybe we just want: >>>> >>>> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c >>>> index 2201b8c78641..0468c6ee4448 100644 >>>> --- a/drivers/video/backlight/pwm_bl.c >>>> +++ b/drivers/video/backlight/pwm_bl.c >>>> @@ -123,6 +123,7 @@ static int pwm_backlight_update_status(struct backlight_device *bl) >>>> if (brightness > 0) { >>>> pwm_get_state(pb->pwm, &state); >>>> state.duty_cycle = compute_duty_cycle(pb, brightness); >>>> + state.enabled = true; >>>> pwm_apply_state(pb->pwm, &state); >>>> pwm_backlight_power_on(pb); >>>> } else >>>> >>>> ? On a side note: It's IMHO strange that pwm_backlight_power_on >>>> reconfigures the PWM once more. >>>> >>> >>> Looking again to the pwm_bl code, now, I am not sure this is correct (although >>> it probably solves the problem for me). >> >> Looking at the pwm_bl code I wouldn't accept the above as it is but I'd >> almost certainly accept a patch to pwm_bl to move the PWM enable/disable >> out of both the power on/off functions so the duty-cycle/enable or >> disable can happen in one go within the update_status function. I don't >> think such a change would interfere with the power and enable sequencing >> needed by panels and it would therefore be a nice continuation of the >> work to convert over to the pwm_apply_state() API. > > OK for me. Enric, do you care enough to come up with a patch for pwm_bl? > I'd expect that this alone should already fix your issue. >
Yes, I'll work on a proposal and send. Thanks you all.
Regards, Enric
>> None of the above has anything to do with what is right or wrong for >> the PWM API evolution. Of course, if this thread does conclude that it >> is OK the duty cycle of a disabled PWM to be retained for some drivers >> and not others then I'd hope to see some WARN_ON()s added to the PWM >> framework to help bring problems to the surface with all drivers. > > I think it's not possible to add a reliable WARN_ON for that issue. It > is quite expected that .get_state returns something that doesn't > completely match the requested configuration. So if a consumer requests > > .duty_cycle = 1 > .period = 100000000 > .enabled = false > > pwm_get_state possibly returns .duty_cycle = 0 even for drivers/hardware > that has a concept of duty_cycle for disabled hardware. > > A bit this is addressed in https://patchwork.ozlabs.org/patch/1147517/. > > Best regards > Uwe >
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