Messages in this thread | | | Date | Tue, 17 Mar 2020 18:52:50 +0100 | From | Pascal Roeleven <> | Subject | Re: pwm: sun4i: pwm-backlight not working since 5.6-rc1 |
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On 2020-03-17 18:32, Uwe Kleine-König wrote: > Hello Pascal, > > On Mon, Mar 16, 2020 at 08:26:13AM +0100, Uwe Kleine-König wrote: >> On Thu, Mar 12, 2020 at 04:06:07PM +0100, Pascal Roeleven wrote: >> > On 2020-03-12 14:29, Uwe Kleine-König wrote: >> > > On Thu, Mar 12, 2020 at 01:22:13PM +0100, Pascal Roeleven wrote: >> > > > Hi all, >> > > > >> > > > I am working on adding an old A10 device to mainline and noticed an >> > > > issue >> > > > when testing on 5.5.8 vs master. >> > > > >> > > > Since 5.6-rc1, I can't control the brightness of my LCD backlight >> > > > anymore. >> > > > The backlight stays on full brightness instead. I am controlling the >> > > > brightness value via sysfs for testing. >> > > > >> > > > I am not sure if this is a general pwm-sun4i issue or if it is >> > > > related to >> > > > the backlight. However I narrowed it down to one commit for pwm-sun4i: >> > > > >> > > > fa4d81784681a26bcf7d2a43c6ac5cf991ef28f5 >> > > > >> > > > If I use pwm-sun4i.c from 5b090b430d750961305030232314b6acdb0102aa on >> > > > master, the backlight works fine. Unfortunately, due to my lack of >> > > > kernel >> > > > experience, I can't see how the commit above broke it. >> > > >> > > Hmm, I cannot see how fa4d81784681a26bcf7d2a43c6ac5cf991ef28f5 breaks >> > > this. Looking at the output of >> > > >> > > git show -b fa4d81784681a26bcf7d2a43c6ac5cf991ef28f5 >> > > >> > > (i.e. ignoring whitespace changes) I don't see how the behaviour you're >> > > reporting can be explained. >> > > >> > > Are you sure that fa4d81784681a26bcf7d2a43c6ac5cf991ef28f5 is the bad >> > > commit? >> > > >> > > Can you install a tool to inspect register values and check how the >> > > affected registers change if you switch kernel versions and/or pwm >> > > settings? >> > > >> > > (e.g. >> > > memtool md 0x1c20e00+0xc >> > > ) >> > > >> > > Best regards >> > > Uwe >> > >> > Thanks for your response. >> > >> > Yes I am sure that is the commit. If I am on master, and replace pwm-sun4i.c >> > with the one from 5b090b43, everything works. If I then apply fa4d8178, it >> > stops working. >> > >> > And strangely the output of the registers is exactly the same before and >> > after fa4d8178: >> > >> > 01c20e00: 00000050 00130014 00000000 (full brightness) >> > 01c20e00: 00000050 00130006 00000000 (min brightness) >> > >> > Even when I'm on 5b090b43 and cherry-pick fa4d8178 can I reproduce the >> > issue. >> >> Very strange. I'm out of sensible ideas. The remaining ones are: >> >> - enable tracing in the kernel and boot with >> >> trace_event=pwm >> >> And then check after the problem occurred in >> /sys/kernel/debug/tracing/trace if something sticks out. >> >> - Try modifying the registers using memtool. E.g. >> >> memtool mw 0x01c20e04 0x00130012 >> >> - Do you have equipment to check the actual output of the PWM >> hardware? >> If so, what do you see? > > I assume the sun4i-series you sent earlier today resolves the problems > you reported here? > > Best regards > Uwe
Hi Uwe,
Yes it does, but as Emil mentioned it's probably not complete. It's just an RFC for now to make sure it doesn't cause a regression. Turns out the Allwinner PWM controller is even more pickier than I thought.
Again, thank you for your help.
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