Created attachment 86557 [details]
dmesg: testdisplay cause call trace

Description:
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After running testdisplay cases(include -a,-d,-p,-t,-f), there's call trace come up in console. No matter we use which kind pipe(VGA or eDP), each of them exists. It's a regression and been bisected.

Bisect result:
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f1f644dc66cbaf5a4c7dcde683361536b41885b9 is the first bad commit
commit f1f644dc66cbaf5a4c7dcde683361536b41885b9
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Thu Jun 27 00:39:25 2013 +0300

    drm/i915: get mode clock when reading the pipe config v9

    We need this for comparing modes between configuration changes.

    The tricky part is to allow us to reuse the new get_clock stuff to
    recover the lvds clock on gen2/3 when neither the vbt has an lvds mode
    nor the panel a (useful) EDID.

    v2: try harder to calulate non-simple pixel clocks (Daniel)
        call get_clock after getting the encoder config, needed for pixel multiply
        (Jesse)
    v3: drop get_clock now that the pixel_multiply has been moved into
        get_pipe_config
    v4: re-add get_clock; we need to get the pixel multiplier in the
        encoder, so need to calculate the clock value after the encoder's
        get_config is called
    v5: drop hsw clock_get, still needs to be written



Reproduce Steps:
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1. boot up machine
2. run testdisplay
3. checkout dmesg