According to BSpec, for ILK and SNB those bits must be programmed to 1 before 
enabling VGA display and kept enable while VGA display is enabled. It says also 
it is safe to have it as 1 even when VGA display is disabled.

Signed-off-by: Rodrigo Vivi <[email protected]>
---
 drivers/gpu/drm/i915/i915_reg.h | 2 ++
 drivers/gpu/drm/i915/intel_pm.c | 8 ++++++++
 2 files changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index f2a5ea6..8314124 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -816,6 +816,8 @@
 #define   ILK_FBC_RT_VALID     (1<<0)
 
 #define ILK_DISPLAY_CHICKEN1   0x42000
+#define   ILK_VRD_REQ_STALL_DIS        (1<<31)
+#define   ILK_VRD_REQ_STALL_TH (1<<29)
 #define   ILK_FBCQ_DIS         (1<<22)
 #define          ILK_PABSTRETCH_DIS    (1<<21)
 
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index abfff29..dfb1be7 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3381,6 +3381,10 @@ static void ironlake_init_clock_gating(struct drm_device 
*dev)
        struct drm_i915_private *dev_priv = dev->dev_private;
        uint32_t dspclk_gate = ILK_VRHUNIT_CLOCK_GATE_DISABLE;
 
+       I915_WRITE(ILK_DISPLAY_CHICKEN1,
+                  I915_READ(ILK_DISPLAY_CHICKEN1) |
+                  ILK_VRD_REQ_STALL_DIS | ILK_VRD_REQ_STALL_TH);
+
        /* Required for FBC */
        dspclk_gate |= ILK_DPFCRUNIT_CLOCK_GATE_DISABLE |
                   ILK_DPFCUNIT_CLOCK_GATE_DISABLE |
@@ -3470,6 +3474,10 @@ static void gen6_init_clock_gating(struct drm_device 
*dev)
 
        I915_WRITE(ILK_DSPCLK_GATE_D, dspclk_gate);
 
+       I915_WRITE(ILK_DISPLAY_CHICKEN1,
+                  I915_READ(ILK_DISPLAY_CHICKEN1) |
+                  ILK_VRD_REQ_STALL_DIS | ILK_VRD_REQ_STALL_TH);
+
        I915_WRITE(ILK_DISPLAY_CHICKEN2,
                   I915_READ(ILK_DISPLAY_CHICKEN2) |
                   ILK_ELPIN_409_SELECT);
-- 
1.7.11.7

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