Commit f5d9b7f0f9 (fix r600_enable_sclk_control()) causes kexec issues

[Markus Trippelsdorf]

On 2013.07.29 at 15:53 -0400, Alex Deucher wrote:
> On Mon, Jul 29, 2013 at 2:10 PM, Eric W. Biederman
> <ebiederm at xmission.com> wrote:
> > Alex Deucher <alexdeucher at gmail.com> writes:
> >
> >> On Mon, Jul 29, 2013 at 11:50 AM, Eric W. Biederman
> >> <ebiederm at xmission.com> wrote:
> >>>
> >>>
> >>> Alex Deucher <alexdeucher at gmail.com> wrote:
> >>>>On Mon, Jul 29, 2013 at 10:09 AM, Markus Trippelsdorf
> >>>><markus at trippelsdorf.de> wrote:
> >>>>> On 2013.07.29 at 09:58 -0400, Alex Deucher wrote:
> >>>>>> On Mon, Jul 29, 2013 at 3:51 AM, Markus Trippelsdorf
> >>>>>> <markus at trippelsdorf.de> wrote:
> >>>>>> > On my test machine Xorg doesn't start anymore when I kexec into a
> >>>>>> > 3.11.0-rc3 kernel.
> >>>>>>
> >>>>>> With kexec, dpm doesn't get torn down properly which can result in a
> >>>>>> bad hardware state when the driver loads again.  Does the attached
> >>>>>> patch help?  It attempts to disable dpm at startup in case it wasn't
> >>>>>> torn down properly previously.
> >>>>>
> >>>>> dpm initialization now works, but unfortunately GPU acceleration
> >>>>still gets
> >>>>> disabled:
> >>>>
> >>>>Stupid kexec complicates things.  We need to make sure dpm is torn
> >>>>down before we init the rest of the GPU, but dpm needs get initialized
> >>>>later in the init process since it depends on certain other state from
> >>>>the driver.  I need to think about this for a bit.  I'm not sure of a
> >>>>good way to handle this.
> >>>
> >>> You might just want to implement a shutdown method that cleans things up properly.   At least as a first pass until you worry about things like kexec on panic.
> >>>
> >>> Or can you not shutdown the graphics stack on reboot because of the need to display the kernels shutdown progress?
> >>
> >> Does kexec actually call this shutdown method?  The driver implements
> >> appropriate clean-up measures if it's shutdown properly.
> >
> > Absoltuely.  All parts of the reboot path call ->shutdown.  Including
> > kexec.
> >
> > You don't get a device remove/hotunplug but unless this is a kexec on
> > panic ->shutdown is most definitely called.  Now I am talking about the
> > device layer/pci layer shutdown method I don't know how gpu drivers are
> > wired up.  GPU land was a little strange last I looked.  Hopefully it
> > isn't so strange that there is a method named shutdown that is not wired
> > up.
> 
> It doesn't look like the drm infrastructure has a shutdown callback.
> The drm drivers register a drm_driver callback struct that includes an
> unload callback which takes care of all the device teardown (if you
> unload the module for example).  I don't know that it actually gets
> called at kexec time however.  I don't know enough about how kexec
> works.

BTW there is r100_restore_sanity() in drm/radeon/r100.c that explicitly
handles the kexec case during init. So maybe an r600_restore_sanity()
function is needed?

(One of the advantages of using kexec (besides the much quicker boot
time) is that the monitor is not switched off and then on during boot.
I guess that advantage would be lost if the unload callback would be
called.)

-- 
Markus