commit 09be4a52 upstream.

Check to make sure the vblank period is long enough to support
mclk switching.

v2: drop needless initial assignment (Nils)

bug: https://bugs.freedesktop.org/show_bug.cgi?id=96868Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>