drm/i915: HDMI hardware workaround for Ironlake

This brings some hardware workaround for HDMI port on PCH (Ibex Peak),
which fixes unstable issues like during rotation.

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

1 files changed, 22 insertions, 4 deletions

diff --git a/drivers/gpu/drm/i915/intel_hdmi.c b/drivers/gpu/drm/i915/intel_hdmi.c
index 663ab6de0b58..c33451aec1bd 100644
--- a/drivers/gpu/drm/i915/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/intel_hdmi.c
@@ -77,14 +77,32 @@ static void intel_hdmi_dpms(struct drm_encoder *encoder, int mode)
         struct intel_hdmi_priv *hdmi_priv = intel_output->dev_priv;
         u32 temp;
 
-        if (mode != DRM_MODE_DPMS_ON) {
-                temp = I915_READ(hdmi_priv->sdvox_reg);
+        temp = I915_READ(hdmi_priv->sdvox_reg);
+
+        /* HW workaround, need to toggle enable bit off and on for 12bpc, but
+         * we do this anyway which shows more stable in testing.
+         */
+        if (IS_IGDNG(dev)) {
                 I915_WRITE(hdmi_priv->sdvox_reg, temp & ~SDVO_ENABLE);
+                POSTING_READ(hdmi_priv->sdvox_reg);
+        }
+
+        if (mode != DRM_MODE_DPMS_ON) {
+                temp &= ~SDVO_ENABLE;
         } else {
-                temp = I915_READ(hdmi_priv->sdvox_reg);
-                I915_WRITE(hdmi_priv->sdvox_reg, temp | SDVO_ENABLE);
+                temp |= SDVO_ENABLE;
         }
+
+        I915_WRITE(hdmi_priv->sdvox_reg, temp);
         POSTING_READ(hdmi_priv->sdvox_reg);
+
+        /* HW workaround, need to write this twice for issue that may result
+         * in first write getting masked.
+         */
+        if (IS_IGDNG(dev)) {
+                I915_WRITE(hdmi_priv->sdvox_reg, temp);
+                POSTING_READ(hdmi_priv->sdvox_reg);
+        }
 }
 
 static void intel_hdmi_save(struct drm_connector *connector)