[Intel-gfx] Reverted commit - why?

[Peter Clifton]

Just wondering what was bad about the patch reverted by this commit?


    Revert "drm/i915: Configure the TV sense state correctly on GM45 to make TV detection reliable"
    
    Eric mentioned on irc this patch was bad, so revert it.
    
    This reverts commit fb8b5a39b6310379d7b54c0c7113703a8eaf4a57.
    
    Acked-by: Eric Anholt <eric at anholt.net>
    Signed-off-by: Dave Airlie <airlied at redhat.com>

----------------------- drivers/gpu/drm/i915/intel_tv.c -----------------------
index 081cb90..6d553c2 100644
@@ -1263,15 +1263,6 @@ intel_tv_detect_type (struct drm_crtc *crtc, struct intel_encoder *intel_encoder
 		   DAC_A_0_7_V |
 		   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);
 	intel_wait_for_vblank(dev);


Log for the patch was:

    drm/i915: Configure the TV sense state correctly on GM45 to make TV detection reliable
    
    The TV detection logic is not reliable on the Cantiga platform.
    Sometimes the TV will be misdetected as the following two cases:
    - TV is misdetected on some laptops. e.g. There is no TV connector
    port or no TV is attached. But the TV is shown as connected.
    - TV connector type is misdetected. e.g. the component TV is
    attached, but the TV is shown as S-video type.
    
    According to the hardware requirement, the TV sense state bits of TV DAC
    register should be cleared to zero on Cantiga platfrom.
    
    https://bugzilla.kernel.org/show_bug.cgi?id=14792
    
    Cc: Stable Team <stable at kernel.org>
    Signed-off-by: Zhao Yakui <yakui.zhao at intel.com>
    Tested-by: Santi <santi at agolina.net>
    Signed-off-by: Zhenyu Wang <zhenyuw at linux.intel.com>
    Signed-off-by: Eric Anholt <eric at anholt.net>


Just wondering, since this fix prevented spurious mis-detection of
connected TV-out on my GM45 laptop.

-- 
Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,
Cambridge
CB3 0FA

Tel: +44 (0)7729 980173 - (No signal in the lab!)
Tel: +44 (0)1223 748328 - (Shared lab phone, ask for me)