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: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/i915_suspend.c b/drivers/gpu/drm/i915/i915_suspend.c
index 0ede02a99d914544d145b043b1ea066b5254bb02..a748e5cabe14e1e3ca4550db29078e0c45464682 100644 (file)
--- 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);