linux-kernel - Re: [PATCH] Revert "drm/i915: fix vblank wait test condition"

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Date:	Sat, 4 Sep 2010 12:54:38 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Pekka Enberg <penberg@...nel.org>
cc:	Chris Wilson <chris@...is-wilson.co.uk>,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sitsofe Wheeler <sitsofe@...oo.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [PATCH] Revert "drm/i915: fix vblank wait test condition"

On Sat, 4 Sep 2010, Pekka Enberg wrote:
> On Sat,  4 Sep 2010 11:17:14 +0300, Pekka Enberg <penberg@...nel.org> wrote:
> >> This reverts commit 9559fcdbff4f93d29af04478bbc48294519424f5. The commit causes
> >> wrong screen resolution on some i915 machines such as MacBook which is a
> >> regression from 2.6.35. The issue has been reported multiple times but no fix
> >> has emerged:
> 
> On Sat, Sep 4, 2010 at 12:21 PM, Chris Wilson <chris@...is-wilson.co.uk> wrote:
> > NAK. You can't simply hide one bug by introducing a much bigger one.
> 
> Dude, it's a nasty regression from 2.6.35. What exactly are you NAK'ing here?
> 
> > As you have an affected machine, find which wait_for_vblank() needs to be
> > replaced with a msleep(20|50).
> 
> The attached patch fixes things here. I'm not a drm developer so I
> don't know if it makes technical sense.

Many thanks to you, Pekka: I also don't know if it makes technical sense,
but it solves the same issue for me, so I can at last use 2.6.36-rc on
this laptop.  I sure hope this or an equivalent makes it into -rc4.

Hugh

From 53e5840a6abb50f12f9d2b32efa2a472b203d52f Mon Sep 17 00:00:00 2001
From: Pekka Enberg <penberg@...nel.org>
Date: Sat, 4 Sep 2010 19:24:04 +0300
Subject: [PATCH] i915: Fix wrong resolution after boot problem

Signed-off-by: Pekka Enberg <penberg@...nel.org>
---
 drivers/gpu/drm/i915/intel_tv.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_tv.c b/drivers/gpu/drm/i915/intel_tv.c
index d2029ef..7784ff8 100644
--- a/drivers/gpu/drm/i915/intel_tv.c
+++ b/drivers/gpu/drm/i915/intel_tv.c
@@ -1231,7 +1231,6 @@ intel_tv_detect_type (struct intel_tv *intel_tv)
 	struct drm_encoder *encoder = &intel_tv->base.enc;
 	struct drm_device *dev = encoder->dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	struct intel_crtc *intel_crtc = to_intel_crtc(encoder->crtc);
 	unsigned long irqflags;
 	u32 tv_ctl, save_tv_ctl;
 	u32 tv_dac, save_tv_dac;
@@ -1268,11 +1267,11 @@ intel_tv_detect_type (struct intel_tv *intel_tv)
 		   DAC_C_0_7_V);
 	I915_WRITE(TV_CTL, tv_ctl);
 	I915_WRITE(TV_DAC, tv_dac);
-	intel_wait_for_vblank(dev, intel_crtc->pipe);
+	msleep(20);
 	tv_dac = I915_READ(TV_DAC);
 	I915_WRITE(TV_DAC, save_tv_dac);
 	I915_WRITE(TV_CTL, save_tv_ctl);
-	intel_wait_for_vblank(dev, intel_crtc->pipe);
+	msleep(20);
 	/*
 	 *  A B C
 	 *  0 1 1 Composite
-- 
1.6.3.3