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 -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ | -- You received this message because you are subscribed to the Google Groups "linux-sunxi" group. To unsubscribe from this group and stop receiving emails from it, send an email to linux-sunxi+unsubscr...@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/linux-sunxi/20200317173208.t5s63pfz3byxsgzi%40pengutronix.de.
