Re: [PATCH] drm/amdgpu: fix regression on CIK (v2)

[Ben Hutchings <ben@decadent.org.uk>]

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On Sun, 2016-04-10 at 09:22 -0700, Greg KH wrote:
> On Tue, Mar 22, 2016 at 04:31:30PM -0400, Alex Deucher wrote:
> > 
> > On Tue, Mar 22, 2016 at 4:27 PM, Greg KH  wrote:
> > > 
> > > On Tue, Mar 22, 2016 at 04:14:30PM -0400, Alex Deucher wrote:
> > > > 
> > > > On Tue, Mar 22, 2016 at 4:11 PM, Greg KH  wrote:
> > > > > 
> > > > > On Tue, Mar 22, 2016 at 03:48:18PM -0400, Alex Deucher wrote:
> > > > > > 
> > > > > > From: Grigori Goronzy <greg@chown.ath.cx>
> > > > > > 
> > > > > > This fix was written against drm-next, but when it was
> > > > > > backported to 4.5 as a stable fix, the driver internal
> > > > > > structure change was missed.  Fix that up here to avoid
> > > > > > a hang due to waiting for the wrong sequence number.
> > > > > > 
> > > > > > v2: agd: fix up commit message
> > > > > > 
> > > > > > Signed-off-by: Grigori Goronzy <greg@chown.ath.cx>
> > > > > > Cc: stable@vger.kernel.org
> > > > > > Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
> > > > > > ---
> > > > > > 
> > > > > > Hi Greg,
> > > > > > 
> > > > > > The code is correct for 4.6, this fix should be applied to
> > > > > > 4.5 and older stable kernels.
> > > > > What is the patch in 4.6 that made it "correct"?  I would much rather
> > > > > take that than something else.
> > > > It's correct as is for 4.6.  I cherry-picked it out of my drm-next
> > > > tree into 4.5 since it was a bug fix, but missed the internal driver
> > > > structure change in drm-next that was not in 4.5.
> > > I'm sorry, I don't understand at all what you mean here :(
> > > 
> > > What changed between 4.5.0 and 4.6-rc1 that made 4.5 "broken"?  What
> > > fixed it in 4.6-rc1?
> > The patch was written and tested against drm-next, but I cherry-picked
> > it to 4.5 as is since it was a bug fix.  However, I missed the
> > internal driver structure change that it depended on.  Now that
> > drm-next has been merged into 4.6 (including the driver structure
> > change), the code from 4.5 works fine.  However 4.5 and older kernels
> > are broken since they don't have the changes for 4.6.
> I still don't understand.  What is the commit in Linus's tree that
> matches this change?

This commit changed amdgpu_fence_driver::sync_seq from an array to a
scalar:

commit 5907a0d8af71d17811be49f2c056b3a89660e188
Author: Christian König <christian.koenig@amd.com>
Date:   Mon Jan 18 15:16:53 2016 +0100

    drm/amdgpu: cleanup sync_seq handling

> Why can't I just cherry-pick that patch instead of
> this "custom" one?
[...]

Looks like it depends on other changes to lock usage.

Ben.

-- 
Ben Hutchings
The generation of random numbers is too important to be left to chance.
                                                            - Robert Coveyou

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