[Bug 76345] New: [Bisected BDW drm-intel-fixes] Enable PSR feature by insert kernel parameter "i915.enable_psr=1", will cause x fail to start

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=76345

          Priority: medium
            Bug ID: 76345
                CC: intel-gfx-bugs at lists.freedesktop.org
          Assignee: intel-gfx-bugs at lists.freedesktop.org
           Summary: [Bisected BDW drm-intel-fixes] Enable PSR feature by
                    insert kernel parameter "i915.enable_psr=1", will
                    cause x fail to start
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: major
    Classification: Unclassified
                OS: Linux (All)
          Reporter: wendy.wang at intel.com
          Hardware: x86 (IA32)
            Status: NEW
           Version: unspecified
         Component: DRM/Intel
           Product: DRI

By kernel default setting, PSR feature is false, we need insert
"i915.enable_psr=1" parameter in kernel to enable the PSR in kernel, after
reboot, run xinit &, x fail to start.

this issue happened from 2014_03_07 nightly branch to the latest nightly
branch, before that no such issue.

Do bisect find  drm-intel-fixes branch,
24bd9bf54d45d28089251cdf62bf14323d1aa827 is the first bad commit, revert this
commit, issue disappeared.

This issue found on BDW platform, did not reproduce on HSW platform.

commit 24bd9bf54d45d28089251cdf62bf14323d1aa827
Author: Ben Widawsky <benjamin.widawsky at intel.com>
Date:   Tue Mar 4 22:38:10 2014 -0800

    drm/i915: Fix PSR programming

    | has a higher precedence than ?. Therefore, the calculation doesn't do
    at all what you would expect. Thanks to Ken for convincing me that this
    was indeed the issue. Send me back to C programmer school, please.

    I'm sort of surprised PSR was continuing to work for people. It should
    be broken IMO (and it was broken for me, but I had assumed it never
    worked).

    Regression from:
    commit ed8546ac1f99b850879f07b1e9b06b42fb0a36d9
    Author: Ben Widawsky <benjamin.widawsky at intel.com>
    Date:   Mon Nov 4 22:45:05 2013 -0800

        drm/i915/bdw: Support eDP PSR

    Cc: Rodrigo Vivi <rodrigo.vivi at gmail.com>
    Cc: Kenneth Graunke <kenneth.w.graunke at intel.com>
    Cc: Art Runyan <arthur.j.runyan at intel.com>
    Reported-by: "Kumar, Kiran S" <kiran.s.kumar at intel.com>
    Cc: stable at vger.kernel.org [v3.13+]
    Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
    Signed-off-by: Jani Nikula <jani.nikula at intel.com>

:040000 040000 af3b065bcd133817f46c1c1e6328db8cc1767095
c7b6f61027f166bb5a712201a2bd2d3997adac6e M      drivers

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