intel_display.c: ensures the sync polarity to the panel is correct
and issues a message if the driver changes it. 

If these are not correct then although the panel looks ok, output from an HDMI
encoder (eg, Chrontel CH7036) will be incorrect. 

Signed-off-by: Mark Hayter <[email protected]>

Index: drivers/gpu/drm/i915/i915_reg.h
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 
b463a0baa924ff1dee74ca8473b458927cfa0901..e325eaea4bfb289c76a093c5cada026eab6c3983
 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -1056,6 +1056,10 @@
 #define   LVDS_PIPEB_SELECT            (1 << 30)
 /* LVDS dithering flag on 965/g4x platform */
 #define   LVDS_ENABLE_DITHER           (1 << 25)
+/* LVDS sync polarity flags. Set to invert (i.e. negative) */
+#define   LVDS_VSYNC_POLARITY          (1 << 21)
+#define   LVDS_HSYNC_POLARITY          (1 << 20)
+
 /* Enable border for unscaled (or aspect-scaled) display */
 #define   LVDS_BORDER_ENABLE           (1 << 15)
 /*
Index: drivers/gpu/drm/i915/intel_display.c
diff --git a/drivers/gpu/drm/i915/intel_display.c 
b/drivers/gpu/drm/i915/intel_display.c
index 
787e6da01984a2c2296295359250cd436e0cf5fe..9893e53e394cc9140167b9884c05efd62c4f139c
 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3334,6 +3334,29 @@ static int intel_crtc_mode_set(struct drm_crtc *crtc,
                                        lvds &= ~LVDS_ENABLE_DITHER;
                        }
                }
+               /* Only tested on pineview, should work on IS_9XX */
+               if (IS_PINEVIEW(dev)) {
+                       /* Set sync polarity for case when vbios did not */
+                       char curhs, curvs, newhs, newvs;
+                       curhs = (lvds & LVDS_HSYNC_POLARITY) ? '-' : '+';
+                       curvs = (lvds & LVDS_VSYNC_POLARITY) ? '-' : '+';
+                       newhs = (adjusted_mode->flags & DRM_MODE_FLAG_NHSYNC) ?
+                               '-' : '+';
+                       newvs = (adjusted_mode->flags & DRM_MODE_FLAG_NVSYNC) ?
+                               '-' : '+';
+                       if ((newhs != curhs) || (newvs != curvs)) {
+                               DRM_INFO("Change lvds panel from %chsync "
+                                        "%cvsync to %chsync %cvsync\n",
+                                        curhs, curvs, newhs, newvs);
+                               /* Clear to both + polarity */
+                               lvds &= ~(LVDS_HSYNC_POLARITY |
+                                         LVDS_VSYNC_POLARITY);
+                               if (newhs == '-')
+                                       lvds |= LVDS_HSYNC_POLARITY;
+                               if (newvs == '-')
+                                       lvds |= LVDS_VSYNC_POLARITY;
+                       }
+               }
                I915_WRITE(lvds_reg, lvds);
                I915_READ(lvds_reg);
        }
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