drm/i915: Select the correct BPC for LVDS on Ironlake

Select the correct BPC for LVDS on Ironlake. If it is 18-bit LVDS panel,
the BPC will be 6. When it is 24-bit LVDS panel, the BPC will 8.
At the same time the BPC will be 8 when the output device is CRT/HDMI/DP.

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

1 files changed, 12 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 63e8e9fd6793..5e2159b59920 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2993,6 +2993,18 @@ static int intel_crtc_mode_set(struct drm_crtc *crtc,
 
                 /* determine panel color depth */
                 temp = I915_READ(pipeconf_reg);
+                temp &= ~PIPE_BPC_MASK;
+                if (is_lvds) {
+                        int lvds_reg = I915_READ(PCH_LVDS);
+                        /* the BPC will be 6 if it is 18-bit LVDS panel */
+                        if ((lvds_reg & LVDS_A3_POWER_MASK) == LVDS_A3_POWER_UP)
+                                temp |= PIPE_8BPC;
+                        else
+                                temp |= PIPE_6BPC;
+                } else
+                        temp |= PIPE_8BPC;
+                I915_WRITE(pipeconf_reg, temp);
+                I915_READ(pipeconf_reg);
 
                 switch (temp & PIPE_BPC_MASK) {
                 case PIPE_8BPC: