[PATCH 0/3] drm/radeon kexec fixes

Markus Trippelsdorf markus at trippelsdorf.de
Wed Sep 11 02:01:35 PDT 2013

On 2013.09.09 at 11:38 +0200, Christian König wrote:
> Am 09.09.2013 11:21, schrieb Markus Trippelsdorf:
> > On 2013.09.08 at 17:32 -0700, Eric W. Biederman wrote:
> >> Markus Trippelsdorf <markus at trippelsdorf.de> writes:
> >>
> >>> Here are a couple of patches that get kexec working with radeon devices.
> >>> I've tested this on my RS780.
> >>> Comments or flames are welcome.
> >>> Thanks.
> >> A couple of high level comments.
> >>
> >> This looks promising for the usual case.
> >>
> >> Removing the printk at the end of the kexec path seems a little dubious,
> >> what of other cpus, interrupt handlers, etc.  Basically estabilishing a
> >> new rule on when printk is allowed seems a little dubious at this point,
> >> even if it is a useful debugging trick.
> > OK. I will drop this patch. It doesn't seem to be necessary, because I
> > cannot reproduce the printk related hang anymore.
> >
> >> Having a clean shutdown of the radeon definitely seems worth doing,
> >> because the cases where we care abouty video are when a person is in
> >> front of the system.
> > Yes. But please note that even with radeon_pci_shutdown implemented, I
> > still get ring test failures on roughly every eighth kexec boot:
> >
> >   [drm:r600_dma_ring_test] *ERROR* radeon: ring 3 test failed (0xCAFEDEAD)
> >   radeon 0000:01:05.0: disabling GPU acceleration
> >
> > That's definitely better than the current state of affairs, with ring
> > test failures on every second boot. But I haven't figured out the reason
> > for these failures yet. It's curious that once a ring test failure
> > occurs, it will reliably fail after each kexec invocation, no matter how
> > often repeated. Only a reboot brings the machine back to normal.
> The main problem here is that the AMD gfx hardware doesn't really 
> support being reinitialized once booted (for various reasons). It's a 
> (intended) limitation of the hardware design that you can only 
> initialize certain blocks once every power cycle, so the whole approach 
> actually will never work 100% reliable.
> All you can hope for is that stopping the hardware while shutting down 
> the old kernel and starting it again results in exactly the same 
> hardware parameters (offsets, clock etc...) otherwise starting the 
> blocks will just fail and you end up with disabled acceleration like above.
> Sorry, but there isn't much we can do about this,

I've tested this further and it turned out that if I revert commit
f5d9b7f0f9 on top of my "drm/radeon: Implement radeon_pci_shutdown"
patch, the initialization failures seem to go away completely.

Any idea what's going on?

Here's the patch:

diff --git a/drivers/gpu/drm/radeon/r600_dpm.c b/drivers/gpu/drm/radeon/r600_dpm.c
index fa0de46..4e8c1988 100644
--- a/drivers/gpu/drm/radeon/r600_dpm.c
+++ b/drivers/gpu/drm/radeon/r600_dpm.c
@@ -296,9 +296,9 @@ bool r600_dynamicpm_enabled(struct radeon_device *rdev)
 void r600_enable_sclk_control(struct radeon_device *rdev, bool enable)
 	if (enable)
 void r600_enable_mclk_control(struct radeon_device *rdev, bool enable)


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