drm/i915: Fix eDP blank screen after S3 resume on HP desktops

commit 6db65cbb941f9d433659bdad02b307f6d94465df upstream.

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

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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 bc7dcaa1c68..5ad0b5124b7 100644
--- a/drivers/gpu/drm/i915/i915_suspend.c
+++ b/drivers/gpu/drm/i915/i915_suspend.c
@@ -739,8 +739,11 @@ 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);