linux-kernel - [PATCH 096/222] drm/i915: drop buggy write to FDI_RX

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Message-Id: <1358351822-7675-97-git-send-email-herton.krzesinski@canonical.com>
Date:	Wed, 16 Jan 2013 13:54:56 -0200
From:	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Jani Nikula <jani.nikula@...el.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
Subject: [PATCH 096/222] drm/i915: drop buggy write to FDI_RX_CHICKEN register

3.5.7.3 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Vetter <daniel.vetter@...ll.ch>

commit 607a6f7a6621f65706ff536b2615ee65b5c2f575 upstream.

Jani Nikula noticed that the parentheses are wrong and we & the bit
with the register address instead of the read-back value. He sent a
patch to correct that.

On second look, we write the same register in the previous line, and
the w/a seems to be to set FDI_RX_PHASE_SYNC_POINTER_OVR to enable the
logic, then keep always set FDI_RX_PHASE_SYNC_POINTER_OVR and toggle
FDI_RX_PHASE_SYNC_POINTER_EN before/after enabling the pc transcoder.

So the right things seems to be to simply kill the 2nd write.

Cc: Jani Nikula <jani.nikula@...el.com>
Reviewed-by: Chris Wilson <chris@...is-wilson.co.uk>
[danvet: Dropped a bogus ~ from the commit message that somehow crept
in.]
Signed-off-by: Daniel Vetter <daniel.vetter@...ll.ch>
[ herton: this looks a good bug fix, which also makes the next patch,
 "drm/i915: disable cpt phase pointer fdi rx workaround", easier to apply ]
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
---
 drivers/gpu/drm/i915/intel_display.c |    3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index c69444a..98ea04e 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2609,9 +2609,6 @@ static void ironlake_fdi_disable(struct drm_crtc *crtc)
 	/* Ironlake workaround, disable clock pointer after downing FDI */
 	if (HAS_PCH_IBX(dev)) {
 		I915_WRITE(FDI_RX_CHICKEN(pipe), FDI_RX_PHASE_SYNC_POINTER_OVR);
-		I915_WRITE(FDI_RX_CHICKEN(pipe),
-			   I915_READ(FDI_RX_CHICKEN(pipe) &
-				     ~FDI_RX_PHASE_SYNC_POINTER_EN));
 	} else if (HAS_PCH_CPT(dev)) {
 		cpt_phase_pointer_disable(dev, pipe);
 	}
-- 
1.7.9.5

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