drm/i915: Do not clobber the contents of TRANS_DP_CTL when enabling.

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

2 files changed, 5 insertions, 3 deletions

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 281db6e5403a..97a35a42da28 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -2928,6 +2928,7 @@
 #define  TRANS_DP_VSYNC_ACTIVE_LOW      0
 #define  TRANS_DP_HSYNC_ACTIVE_HIGH     (1<<3)
 #define  TRANS_DP_HSYNC_ACTIVE_LOW      0
+#define  TRANS_DP_SYNC_MASK     (3<<3)
 
 /* SNB eDP training params */
 /* SNB A-stepping */
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 1490a8c14d26..c7f19ec88f98 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2097,9 +2097,10 @@ static void ironlake_crtc_dpms(struct drm_crtc *crtc, int mode)
                                 int reg;
 
                                 reg = I915_READ(trans_dp_ctl);
-                                reg &= ~TRANS_DP_PORT_SEL_MASK;
-                                reg = TRANS_DP_OUTPUT_ENABLE |
-                                      TRANS_DP_ENH_FRAMING;
+                                reg &= ~(TRANS_DP_PORT_SEL_MASK |
+                                         TRANS_DP_SYNC_MASK);
+                                reg |= (TRANS_DP_OUTPUT_ENABLE |
+                                        TRANS_DP_ENH_FRAMING);
 
                                 if (crtc->mode.flags & DRM_MODE_FLAG_PHSYNC)
                                       reg |= TRANS_DP_HSYNC_ACTIVE_HIGH;