Regression: drm/radeon: brightness control hard system lockup

[Eldad Zack]

On Mon, 14 Jan 2013, Alex Deucher wrote:
> On Sun, Jan 13, 2013 at 4:00 PM, Eldad Zack <eldad at fogrefinery.com> wrote:
> >
> > On Mon, 7 Jan 2013, Alex Deucher wrote:
> >> On Mon, Jan 7, 2013 at 4:33 PM, Eldad Zack <eldad at fogrefinery.com> wrote:
> >> >
> >> > On Mon, 7 Jan 2013, Alex Deucher wrote:
> >> >> On Sun, Jan 6, 2013 at 7:59 AM, Eldad Zack <eldad at fogrefinery.com> wrote:
> >> >> >
> >> >> > Hi Alex,
> >> >> >
> >> >> > Commit 0ecebb9e0d14e9948e0b1529883a776758117d6f "drm/radeon: switch to a
> >> >> > finer grained reset for evergreen" introduced a hard system lockup to my
> >> >> > setup. I found it after bisecting, and confirmed it by reverting it on
> >> >> > the latest mainline ( 5f243b9 ).
> >> >> >
> >> >> > This:
> >> >> >
> >> >> >    echo 7 > /sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/backlight/acpi_video0/brightness
> >> >> >
> >> >> > Causes a hard lock-up hard, i.e. immediate freeze, without any logs.
> >> >> >
> >> >> > See lspci output and kernel .config below.
> >> >> > If there's any more info I can provide, please let me know.
> >> >>
> >> >> Do you normally see GPU resets when changing the backlight?  Please
> >> >> attach your dmesg output when changing the backlight with the patch
> >> >> reverted.
> >> >
> >> > I see nothing. Just to make sure, I cleared the buffer, cycled through
> >> > 0-7 a couple of hunderd times (until the flicker annoyed), but I see no
> >> > messages at all.
> >> > Is there any debug config I should turn on?
> >>
> >> Can you try adding a printk() in evergreen_asic_reset() and see if it
> >> is somehow getting called when you change the brightness?  When you
> >> use the apci backlight control, the radeon driver is not involved at
> >> all.  They only way the driver would get involved is if the acpi
> >> backlight control somehow caused the GPU to hang and then the driver
> >> detected the hang and attempted to reset the GPU.  I don't see any
> >> evidence of a GPU reset in your kernel log however.  Note that the
> >> driver also registers native backlight contol.  Does that work any
> >> better than acpi?
> >
> > The native backlight controls work very well. Thanks for that, I didn't
> > even noticed that. It has finer control over brightness too.
> >
> > I worked out a fix for the problem, but I think it's not a proper one.
> > What I noticed is that evergreen_gpu_soft_reset() is only ever called
> > once on my system, at boot.
> > Then I realized from the dmesg that neither
> > evergreen_gpu_soft_reset_dma() nor evergreen_gpu_soft_reset_gfx() actually
> > do anything. Both return on the first if statements there.
> >
> > So as far as I can tell, the difference your patch introduced is calling
> > evergreen_mc_stop() and evergreen_mc_resume(), which somehow puts my
> > system in some state that ACPI brightness control leads to a lock up.
> >
> > BTW, I don't see a GPU reset happening at all - I also tried suspend/resume
> > and starting an OpenGL application. Do you know how I can trigger it?
> >
> > To fix this, I moved the GUI_ACTIVE test before evergreen_mc_stop(), but
> > I think it just masks the issue.
> > Patch below (against latest HEAD) just in case.
> >
> 
> Thanks for tracking this down.  The attached patch should fix the
> issue properly.

Thanks, I just applied it and it works as expected.

Tested-by: Eldad Zack <eldad at fogrefinery.com>

@Paul: Thanks for the comments, will do so in the future.

Cheers,
Eldad