The bisection between mesa-13.0.0 and mesa-12.0.4 leads to

1fb4179f927442354f93dfc8494f0236e50af838 is the first bad commit
commit 1fb4179f927442354f93dfc8494f0236e50af838
Author: Jan Vesely <jan.vesely@rutgers.edu>
Date:   Thu Jun 9 23:01:46 2016 -0400

    vl: Fix trivial sign compare warnings

    v2: add whitepace fixes

    Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
    Acked-by: Jose Fonseca <jfonseca@vmware.com>
    [Emil Velikov: squash a few more whitespace issues]
    Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

Indeed, reverting just this commit on top of 13.0.0 makes the vdpau hardware
video output for the mpeg2video codec work again with r600 on my HP Pavilion
dv7.