Hello Abel, On Thu, Feb 27, 2025 at 04:26:14PM +0200, Abel Vesa wrote: > On 25-02-27 10:58:47, Uwe Kleine-König wrote: > > Can you please enable CONFIG_PWM_DEBUG, enable pwm tracing ( > > > > echo 1 > /sys/kernel/debug/tracing/events/pwm/enable > > > > ) then reproduce the problem and provide the output of > > > > cat /sys/kernel/debug/tracing/trace > > > > . > > $ cat trace > # tracer: nop > # > # entries-in-buffer/entries-written: 13/13 #P:12 > # > # _-----=> irqs-off/BH-disabled > # / _----=> need-resched > # | / _---=> hardirq/softirq > # || / _--=> preempt-depth > # ||| / _-=> migrate-disable > # |||| / delay > # TASK-PID CPU# ||||| TIMESTAMP FUNCTION > # | | | ||||| | | > modprobe-203 [000] ..... 0.938668: pwm_get: pwmchip0.0: period=1066407 duty_cycle=533334 polarity=0 enabled=1 err=0 > modprobe-203 [000] ..... 0.938775: pwm_apply: pwmchip0.0: period=5000000 duty_cycle=0 polarity=0 enabled=1 err=0 > modprobe-203 [000] ..... 0.938821: pwm_get: pwmchip0.0: period=4266537 duty_cycle=0 polarity=0 enabled=1 err=0 > modprobe-203 [000] ..... 0.938936: pwm_apply: pwmchip0.0: period=4266537 duty_cycle=0 polarity=0 enabled=1 err=0 > modprobe-203 [000] ..... 0.938982: pwm_get: pwmchip0.0: period=4266537 duty_cycle=0 polarity=0 enabled=1 err=0 > modprobe-203 [000] ..... 0.939274: pwm_apply: pwmchip0.0: period=5000000 duty_cycle=921458 polarity=0 enabled=1 err=0 > modprobe-203 [000] ..... 0.939320: pwm_get: pwmchip0.0: period=4266537 duty_cycle=921355 polarity=0 enabled=1 err=0 > modprobe-203 [000] ..... 0.939434: pwm_apply: pwmchip0.0: period=4266537 duty_cycle=921355 polarity=0 enabled=1 err=0 > modprobe-203 [000] ..... 0.939480: pwm_get: pwmchip0.0: period=4266537 duty_cycle=921355 polarity=0 enabled=1 err=0 > systemd-backlig-724 [006] ..... 9.079538: pwm_apply: pwmchip0.0: period=5000000 duty_cycle=5000000 polarity=0 enabled=1 err=0 > systemd-backlig-724 [006] ..... 9.079585: pwm_get: pwmchip0.0: period=4266537 duty_cycle=4266537 polarity=0 enabled=1 err=0 > systemd-backlig-724 [006] ..... 9.079698: pwm_apply: pwmchip0.0: period=4266537 duty_cycle=4266537 polarity=0 enabled=1 err=0 > systemd-backlig-724 [006] ..... 9.079750: pwm_get: pwmchip0.0: period=4266537 duty_cycle=4266537 polarity=0 enabled=1 err=0 > $ > > > > > I didn't take a deeper dive in this driver combination, but here is a > > description about what *should* happen: > > > > You're talking about period in MHz, the PWM abstraction uses > > nanoseconds. So your summary translated to the PWM wording is (to the > > best of my understanding): > > > > 1. PWM backlight driver requests PWM with .period = 200 ns and > > .duty_cycle = 200 ns. > > > > 2. leds-qcom-lpg cannot pick 200 ns exactly and then chooses .period = > > 1000000000 / 4.26666 MHz = 234.375 ns > > > > 3. leds-qcom-lpg then determines setting for requested .duty_cycle > > based on .period = 200 ns which then ends up with something bogus. The trace looks better than what I expected. 2. is fine here because it seems when Sebastian wrote "driver requests PWM with 5 MHz period" that meant period = 5000000 ns. That was then rounded down to 4266537 ns. And the request for period = 5000000 ns + duty_cycle = 5000000 ns was serviced by configuring period = 4266537 ns + duty_cycle = 4266537 ns. So that's a 100 % relative duty configuration as intended. So just from the traces I don't spot a problem. Do these logs not match what actually happens on the signal? Best regards Uwe
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