Bug 40034

Summary:	E-350 misprocesses shader
Product:	Mesa	Reporter:	Lauri Kasanen <cand>
Component:	Drivers/Gallium/r600	Assignee:	Default DRI bug account <dri-devel>
Status:	RESOLVED FIXED	QA Contact:
Severity:	normal
Priority:	medium	CC:	nock
Version:	git
Hardware:	x86 (IA32)
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:
Attachments:	Screenshot of the failure Proposed patch

Description Lauri Kasanen 2011-08-12 01:13:54 UTC

Created attachment 50154 [details]
Screenshot of the failure

If you pull from my e350bug branch ( http://cgit.freedesktop.org/~cand/mesa/log/?h=e350bug ) and execute "pp_jimenezmlaa=8 glxgears", you should see a fully white window. What actually happens on the E-350 is attached.


The gist is "a long shader; output = white;", which should always create white, since the shader has no kilp/discard. While this would rarely happen in practise (the glsl compiler would eliminate dead code), this is a clear bug, and I believe this is causing me other grief.

While the branch is based on ~4 weeks old master, the bug is present when merged with today's master.

The kernel I'm on is 3.0.1.

Comment 1 Lauri Kasanen 2011-08-12 01:14:48 UTC

This test succeeds on both softpipe and llvmpipe.

Comment 2 Lauri Kasanen 2011-08-16 04:21:46 UTC

I have isolated this to the loops. Commenting out all BGNLOOP, ENDLOOP, and BRK instructions lets the card produce white.

Comment 3 Lauri Kasanen 2011-08-16 04:50:15 UTC

Tracking further, the bug only shows when there's more than one break inside a loop.

Comment 4 Lauri Kasanen 2011-08-16 05:04:11 UTC

Scratch that, it appears with only one break too (depends on which break you comment out :P)

Comment 5 Lauri Kasanen 2011-08-16 05:52:55 UTC

Created attachment 50268 [details] [review]
Proposed patch

The attached patch fixes this bug. It also lets MLAA work, showing that there are no other showstoppers for it on r600g / e-350.

Note I'm not at all sure this is the right approach, but hey, it works.

Comment 6 Lauri Kasanen 2011-11-04 09:27:15 UTC

This bug doesn't seem to affect r700 - at least my HD4350 works perfectly with all effects on current master (7.12-devel (git-f800a29))

Comment 7 Michel Dänzer 2011-11-07 09:19:59 UTC

Please send the patch to the mesa-dev mailing list for review, preferably with git send-email or at least generated by git format-patch.

Comment 8 Lauri Kasanen 2011-11-08 05:06:44 UTC

I can't; the same function is used for everything from r600 on - I have no idea whether it would break other hw. As mentioned in the comment above, the bug is not there on a r700 dedicated card on master, which casts further doubt on the patch.

It may simply be an issue in Evergreen loop handling elsewhere, but I really do not understand the hw well enough to say that with any certainty.

Comment 9 Alex Deucher 2012-01-24 05:58:00 UTC

Is this still an issue with latest git?  This commit looks relevant:
http://cgit.freedesktop.org/mesa/mesa/commit/?id=d89c96c75dbb9c003e4643942f2cce8d6cd4995b

Comment 10 Lauri Kasanen 2012-01-24 07:11:39 UTC

I can test on the weekend.

Comment 11 Lauri Kasanen 2012-01-27 02:56:11 UTC

Yes, that commit fixes it. Doubly sure, since I had to apply it on top of master from Dec 19 (the last version that builds without xcb).

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