[Bug 89550] [SNB+ Regression]igt/pm_rpm/universal-planes cause call trace

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89550

Paulo Zanoni <przanoni at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEEDINFO                    |ASSIGNED
                 CC|                            |matthew.d.roper at intel.com,
                   |                            |ville.syrjala at linux.intel.c
                   |                            |om

--- Comment #5 from Paulo Zanoni <przanoni at gmail.com> ---
I did some debugging, here is some relevant information:

At pm_rpm.c:test_one_plane() we set a mode in one monitor, then we set a plane
with drmModeSetPlane(), and then we call
disable_or_dpms_all_screens_and_wait(), which, as the name says, disables all
the modes set. It is this final call that triggers the Kernel WARN.

The problem seems to be that, at __intel_set_mode(), we first call
intel_crtc_disable(), which disables everything, calls drm_vblank_off(), and
also flips intel_crtc->atomic.wait_vblank to true.

Later at __intel_set_mode(), we indirectly call intel_finish_crtc_commit(),
which calls intel_wait_for_vblank() if intel_crtc->atomic.wait_vblank is true.
And we get the WARN because we already disabled vblanks in the previous
paragraph.

So a way to "hide" the WARN would be to just change {ivb,ilk}_disable_plane(),
removing the line that sets intel_crtc->atomic.wait_vblank to true. I didn't
check how to do this on SKL.

That said, Matt or Ville, do you have any comments or insights here?

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