drm/i915: Apply display workaround required according to the B-Spec.

Not known to fix any current bugs.

Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

2 files changed, 6 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 09e2a550265..61fe2619bb6 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -2609,6 +2609,8 @@
 #define GTIER   0x4401c
 
 #define ILK_DISPLAY_CHICKEN2    0x42004
+/* Required on all Ironlake and Sandybridge according to the B-Spec. */
+#define  ILK_ELPIN_409_SELECT   (1 << 25)
 #define  ILK_DPARB_GATE (1<<22)
 #define  ILK_VSDPFD_FULL        (1<<21)
 #define ILK_DSPCLK_GATE         0x42020
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 5ab40355684..c41dae5ade3 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -5819,6 +5819,10 @@ void intel_init_clock_gating(struct drm_device *dev)
                                    ILK_CLK_FBC);
                 }
 
+                I915_WRITE(ILK_DISPLAY_CHICKEN2,
+                           I915_READ(ILK_DISPLAY_CHICKEN2) |
+                           ILK_ELPIN_409_SELECT);
+
                 if (IS_GEN5(dev)) {
                         I915_WRITE(_3D_CHICKEN2,
                                    _3D_CHICKEN2_WM_READ_PIPELINED << 16 |