[Bug 84161] New: [ILK Bisected]igt/kms_flip subcases causes "[drm:ilk_display_irq_handler] *ERROR* Pipe A FIFO underrun "

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=84161

          Priority: high
            Bug ID: 84161
                CC: intel-gfx-bugs at lists.freedesktop.org
          Assignee: intel-gfx-bugs at lists.freedesktop.org
           Summary: [ILK Bisected]igt/kms_flip subcases causes
                    "[drm:ilk_display_irq_handler] *ERROR* Pipe A FIFO
                    underrun "
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: jinxianx.guo at intel.com
          Hardware: Other
            Status: NEW
           Version: unspecified
         Component: DRM/Intel
           Product: DRI

==System Environment==
--------------------------
Regression: Yes.

Non-working platforms: ILK

==kernel==
--------------------------
origin/drm-intel-nightly:c5660b4ad395f1e34eacc22cf81c687edfc9c83c(fails)
    drm-intel-nightly: 2014y-09m-19d-18h-12m-22s UTC integration manifest

==Bug detailed description==
-----------------------------
igt/kms_flip subcases causes "[drm:ilk_display_irq_handler] *ERROR* Pipe A FIFO
underrun "

Case list:
igt/kms_flip/2x-flip-vs-expired-vblank
igt/kms_flip/2x-flip-vs-expired-vblank-interruptible

==Reproduce steps==
---------------------------- 
1. ./kms_flip --run-subtest 2x-flip-vs-expired-vblank

==Bisect results form [PRTS][auto-bisect]==
----------------------------
commit cf1a5cccaae1ac843b6042178662820f1fb58dea
Author:     Mario Kleiner <mario.kleiner.de at gmail.com>
AuthorDate: Sat Sep 13 18:25:54 2014 +0200
Commit:     Daniel Vetter <daniel.vetter at ffwll.ch>
CommitDate: Mon Sep 15 15:47:19 2014 +0200

    drm: Don't update vblank timestamp when the counter didn't change

    If we already have a timestamp for the current vblank counter, don't
    update it with a new timestmap. Small errors can creep in between two
    timestamp queries for the same vblank count, which could be confusing to
    userspace when it queries the timestamp for the same vblank sequence
    number twice.

    This problem gets exposed when the vblank disable timer is not used
    (or is set to expire quickly) and thus we can get multiple vblank
    disable<->enable transition during the same frame which would all
    attempt to update the timestamp with the latest estimate.

    Testcase: igt/kms_flip/flip-vs-expired-vblank
    Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
    Reviewed-by: Mario Kleiner <mario.kleiner.de at gmail.com>

    v2:Mario: Trivial rebase on top of current drm-next (13-Sep-2014)
    Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
    Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

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