From 9d0498a2bf7455159b317f19531a3e5db2ecc9c4 Mon Sep 17 00:00:00 2001
From: Jesse Barnes <jbarnes@virtuousgeek.org>
Date: Wed, 18 Aug 2010 13:20:54 -0700
Subject: [PATCH] drm/i915: wait for actual vblank, not just 20ms

Waiting for a hard coded 20ms isn't always enough to make sure a vblank
period has actually occurred, so add code to make sure we really have
passed through a vblank period (or that the pipe is off when disabling).

This prevents problems with mode setting and link training, and seems to
fix a bug like https://bugs.freedesktop.org/show_bug.cgi?id=29278, but
on an HP 8440p instead.  Hopefully also fixes
https://bugs.freedesktop.org/show_bug.cgi?id=29141.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>
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