Hi, On Wed, Feb 26, 2025 at 05:34:50PM +0100, Uwe Kleine-König wrote: > On Wed, Feb 26, 2025 at 05:31:08PM +0200, Abel Vesa wrote: > > The current implementation assumes that the PWM provider will be able to > > meet the requested period, but that is not always the case. Some PWM > > providers have limited HW configuration capabilities and can only > > provide a period that is somewhat close to the requested one. This > > simply means that the duty cycle requested might either be above the > > PWM's maximum value or the 100% duty cycle is never reached. > > If you request a state with 100% relative duty cycle you should get 100% > unless the hardware cannot do that. Which PWM hardware are you using? > Which requests are you actually doing that don't match your expectation? drivers/leds/rgb/leds-qcom-lpg.c (which probably should at least get a MAINTAINERS entry to have you CC'd considering all the PWM bits in it). See the following discussion (I point you to my message in the middle of a thread, which has a summary and probably is a good starting point): https://lore.kernel.org/all/vc7irlp7nuy5yvkxwb5m7wy7j7jzgpg73zmajbmq2zjcd67pd2@cz2dcracta6w/ Greetings, -- Sebastian > > This could be easily fixed if the pwm_apply*() API family would allow > > overriding the period within the PWM state that's used for providing the > > duty cycle. But that is currently not the case. > > I don't understand what you mean here. > > > So easiest fix here is to read back the period from the PWM provider via > > the provider's ->get_state() op, if implemented, which should provide the > > best matched period. Do this on probe after the first ->pwm_apply() op has > > been done, which will allow the provider to determine the best match > > period based on available configuration knobs. From there on, the > > backlight will use the best matched period, since the driver's internal > > PWM state is now synced up with the one from provider. > > [...] > > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c > > index 237d3d3f3bb1a6d713c5f6ec3198af772bf1268c..71a3e9cd8844095e85c01b194d7466978f1ca78e 100644 > > --- a/drivers/video/backlight/pwm_bl.c > > +++ b/drivers/video/backlight/pwm_bl.c > > @@ -525,6 +525,17 @@ static int pwm_backlight_probe(struct platform_device *pdev) > > goto err_alloc; > > } > > > > + /* > > + * The actual period might differ from the requested one due to HW > > + * limitations, so sync up the period with one determined by the > > + * provider driver. > > + */ > > + ret = pwm_get_state_hw(pb->pwm, &pb->pwm->state); > > As a consumer you're not supposed to write to &pb->pwm->state. That's a > layer violation. Please call pwm_get_state_hw() with a struct pwm_state > that you own and save the relevant parts in your driver data. > > > + if (ret && ret != -EOPNOTSUPP) { > > + dev_err(&pdev->dev, "failed to get PWM HW state"); > > + goto err_alloc; > > + } > > + > > memset(&props, 0, sizeof(struct backlight_properties)); > > > > if (data->levels) { > > Best regards > Uwe
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