Messages in this thread | | | Date | Wed, 9 Oct 2019 12:16:37 +0200 | From | Uwe Kleine-König <> | Subject | Re: [PATCH] pwm: cros-ec: Let cros_ec_pwm_get_state() return the last applied state |
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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.
> 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
-- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ |
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