drm/i915: Fix shifted screen on top of LVDS on IVY laptop

The commit [23670b322: drm/i915: CPT+ pch transcoder workaround]
caused a regression on some HP laptops with IvyBridge.  The whole
laptop screen is shifted downward for a few pixels constantly.
The problem appears only on LVDS while DP and VGA seem unaffected.
Also, the problem disappears once when go and back from S3.
(S4 resume still shows the same problem.)

This patch revives the minimum part the commit above dropped.
For fixing this regression, only the setup of CHICKEN2 bit in
cpt_init_clock_gating() is needed.

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

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 522ff05e378959c40dc392d01d86bc5e5d84e67a..42839fc73499214ce46f2bdafface55b1a3c632e 100644 (file)
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3453,6 +3453,11 @@ static void cpt_init_clock_gating(struct drm_device *dev)
        I915_WRITE(SOUTH_DSPCLK_GATE_D, PCH_DPLSUNIT_CLOCK_GATE_DISABLE);
        I915_WRITE(SOUTH_CHICKEN2, I915_READ(SOUTH_CHICKEN2) |
                   DPLS_EDP_PPS_FIX_DIS);
+       /* The below fixes the weird display corruption, a few pixels shifted
+        * downward, on (only) LVDS of some HP laptops with IVY.
+        */
+       for_each_pipe(pipe)
+               I915_WRITE(TRANS_CHICKEN2(pipe), TRANS_CHICKEN2_TIMING_OVERRIDE);
        /* WADP0ClockGatingDisable */
        for_each_pipe(pipe) {
                I915_WRITE(TRANS_CHICKEN1(pipe),