[Bug 93361] New: 12bpc hdmi causes wrong real refresh rate (swapbuffers return time)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=93361

            Bug ID: 93361
           Summary: 12bpc hdmi causes wrong real refresh rate (swapbuffers
                    return time)
           Product: DRI
           Version: DRI git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Keywords: bisected
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: kevmitch at gmail.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org,
                    kevmitch at gmail.com

Created attachment 120472
  --> https://bugs.freedesktop.org/attachment.cgi?id=120472&action=edit
Samsung un40eh5000 edid reported by xrandr --prop

I have a Samsung un40eh5000 tv that I connect to my Ivy Bridge Lenovo T530
laptop via mini display-port to hdmi. I have attached the raw and decoded EDID. 

As of 7a0baa6234468aa387f9b8a1a79dc2a4b4821f67, it seems 12bpc gets enabled on
this setup (though I can't imagine that my machine or my TV actually support
that in real life). Unfortunately, this seems to change the effective refresh
rate as measured between returns from opengl swapbuffers calls for example in
glxgears.

       | glxgears fps   |
       +----------------+
xrandr | before | after |
-------+--------+-------+
23.98  | 24.00  | 23.85 |
24.00  | 24.00  | 24.13 |
29.97  | 30.00  | 29.81 |
30.00  | 30.00  | 30.17 |
59.94  | 60.00  | 60.12 |
60.00  | 60.00  | 60.12 |

This is problematic for displaying video at native frame rates. For example
when the actual refresh rate of 24.00 hz could be achieved, 23.98fps video
would only have to repeat a frame every 50 seconds. Now it must either drop or
repeat one every 7 seconds which is much more noticeable.

This is duplicated from https://bugzilla.kernel.org/show_bug.cgi?id=109141
where I was told to post here instead.

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