drm/i915: Enable/disable the dithering for LVDS based on VBT setting

Enable/disable the dithering for LVDS based on VBT setting. On the 965/g4x
platform the dithering flag is defined in LVDS register. And on the ironlake
the dithering flag is defined in pipeconf register.

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

2 files changed, 18 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index f79b13324fa..149d360d64a 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -975,6 +975,8 @@
 #define   LVDS_PORT_EN                  (1 << 31)
 /* Selects pipe B for LVDS data.  Must be set on pre-965. */
 #define   LVDS_PIPEB_SELECT             (1 << 30)
+/* LVDS dithering flag on 965/g4x platform */
+#define   LVDS_ENABLE_DITHER            (1 << 25)
 /* Enable border for unscaled (or aspect-scaled) display */
 #define   LVDS_BORDER_ENABLE            (1 << 15)
 /*
@@ -1744,6 +1746,8 @@
 
 /* Display & cursor control */
 
+/* dithering flag on Ironlake */
+#define PIPE_ENABLE_DITHER      (1 << 4)
 /* Pipe A */
 #define PIPEADSL                0x70000
 #define PIPEACONF               0x70008
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 84705b7e01e..0c9b79f2ab3 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3195,7 +3195,20 @@ static int intel_crtc_mode_set(struct drm_crtc *crtc,
                  * appropriately here, but we need to look more thoroughly into how
                  * panels behave in the two modes.
                  */
-
+                /* set the dithering flag */
+                if (IS_I965G(dev)) {
+                        if (dev_priv->lvds_dither) {
+                                if (IS_IRONLAKE(dev))
+                                        pipeconf |= PIPE_ENABLE_DITHER;
+                                else
+                                        lvds |= LVDS_ENABLE_DITHER;
+                        } else {
+                                if (IS_IRONLAKE(dev))
+                                        pipeconf &= ~PIPE_ENABLE_DITHER;
+                                else
+                                        lvds &= ~LVDS_ENABLE_DITHER;
+                        }
+                }
                 I915_WRITE(lvds_reg, lvds);
                 I915_READ(lvds_reg);
         }