[Bug 90422] New: [SKL] Many Piglit multisample tests fail

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=90422

            Bug ID: 90422
           Summary: [SKL] Many Piglit multisample tests fail
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/i965
          Assignee: idr at freedesktop.org
          Reporter: neil at linux.intel.com
        QA Contact: intel-3d-bugs at lists.freedesktop.org

Created attachment 115720
  --> https://bugs.freedesktop.org/attachment.cgi?id=115720&action=edit
Screenshot of results from ext_framebuffer_multisample-formats

Lots of Piglit tests for multisampling fail on Skylake. In particular all of
the tests involving ext_framebuffer_multisample-formats and
ext_framebuffer_multisample-accuracy seem to fail.

ext_framebuffer_multisample-formats is interesting because it tests a range of
different formats in a single instance and it's always only the first one that
fails. It doesn't matter what the first format is, ie, if I swap the first two
formats in fbo-formats.h then the new first fails. Even if I duplicate the
first format it still fails on the first one but the second one succeeds.

It sounds like we are missing some cache flush somewhere that maybe just works
itself out after the first format is tested. Indeed if I enable the
always_flush_cache option in .drirc then it is magically fixed.

I think it is related to the MCS buffer because if I force the renderbuffer
format to INTEL_MSAA_LAYOUT_UMS instead of INTEL_MSAA_LAYOUT_CMS then the bug
is also fixed.

The image is the result of the failing test in
ext_framebuffer_multisample-formats. You can see there are artefacts in the
result.

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