[PATCH] drm/i915: reinstate GM45 TV detection fix

[Daniel Vetter <daniel.vetter@ffwll.ch>]

This reverts commmit d4b74bf07873da2e94219a7b67a334fc1c3ce649 which
reverted the origin fix fb8b5a39b6310379d7b54c0c7113703a8eaf4a57.

We have at least 3 different bug reports that this fixes things and no
indication what is exactly wrong with this. So try again.

To make matters slightly more fun, the commit itself was cc: stable
whereas the revert has not been.

Cc: Zhao Yakui <yakui.zhao@intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Eric Anholt <eric@anholt.net>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=16236
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=25913
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=14792
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/intel_tv.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_tv.c b/drivers/gpu/drm/i915/intel_tv.c
index 05f765e..ca12c70 100644
--- a/drivers/gpu/drm/i915/intel_tv.c
+++ b/drivers/gpu/drm/i915/intel_tv.c
@@ -1153,6 +1153,15 @@ intel_tv_detect_type(struct intel_tv *intel_tv,
 		   DAC_B_0_7_V |
 		   DAC_C_0_7_V);
 
+
+	/*
+	 * The TV sense state should be cleared to zero on cantiga platform. Otherwise
+	 * the TV is misdetected. This is hardware requirement.
+	 */
+	if (IS_GM45(dev))
+		tv_dac &= ~(TVDAC_STATE_CHG_EN | TVDAC_A_SENSE_CTL |
+			    TVDAC_B_SENSE_CTL | TVDAC_C_SENSE_CTL);
+
 	I915_WRITE(TV_CTL, tv_ctl);
 	I915_WRITE(TV_DAC, tv_dac);
 	POSTING_READ(TV_DAC);
-- 
1.7.9.1