commit: 6db65cbb941f9d433659bdad02b307f6d94465df
From: Takashi Iwai <[email protected]>
Date: Thu, 21 Jun 2012 15:30:41 +0200
Subject: drm/i915: Fix eDP blank screen after S3 resume on HP desktops

This patch fixes the problem on some HP desktop machines with eDP
which give blank screens after S3 resume.

It turned out that BLC_PWM_CPU_CTL must be written after
BLC_PWM_CPU_CTL2.  Otherwise it doesn't take effect on these
SNB machines.

Tested with 3.5-rc3 kernel.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=49233

Cc: <[email protected]>
Signed-off-by: Takashi Iwai <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
---
 drivers/gpu/drm/i915/i915_suspend.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_suspend.c 
b/drivers/gpu/drm/i915/i915_suspend.c
index 0ede02a..a748e5c 100644
--- a/drivers/gpu/drm/i915/i915_suspend.c
+++ b/drivers/gpu/drm/i915/i915_suspend.c
@@ -740,8 +740,11 @@ static void i915_restore_display(struct drm_device *dev)
        if (HAS_PCH_SPLIT(dev)) {
                I915_WRITE(BLC_PWM_PCH_CTL1, dev_priv->saveBLC_PWM_CTL);
                I915_WRITE(BLC_PWM_PCH_CTL2, dev_priv->saveBLC_PWM_CTL2);
-               I915_WRITE(BLC_PWM_CPU_CTL, dev_priv->saveBLC_CPU_PWM_CTL);
+               /* NOTE: BLC_PWM_CPU_CTL must be written after BLC_PWM_CPU_CTL2;
+                * otherwise we get blank eDP screen after S3 on some machines
+                */
                I915_WRITE(BLC_PWM_CPU_CTL2, dev_priv->saveBLC_CPU_PWM_CTL2);
+               I915_WRITE(BLC_PWM_CPU_CTL, dev_priv->saveBLC_CPU_PWM_CTL);
                I915_WRITE(PCH_PP_ON_DELAYS, dev_priv->savePP_ON_DELAYS);
                I915_WRITE(PCH_PP_OFF_DELAYS, dev_priv->savePP_OFF_DELAYS);
                I915_WRITE(PCH_PP_DIVISOR, dev_priv->savePP_DIVISOR);
-- 
1.7.3.4
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