drm/i915: Honour LVDS sync polarity from EDID

The i915 driver normally assumes the video bios has configured several
of the LVDS panel registers, and it just inherits the values. If the
vbios has not run, several of these will need to be setup. So we need to
check that the LVDS sync polarity is correctly configured per any
available modelines (e.g. EDID) and adjust if not, issuing a warning as
we do.
Signed-off-by: Mark Hayter <mdhayter@chromium.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_reg.h

@@ -1437,6 +1437,10 @@
 #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)
 /*

drivers/gpu/drm/i915/intel_display.c

@@ -4304,6 +4304,7 @@ static int intel_crtc_mode_set(struct drm_crtc *crtc,
 	int ret;
 	struct fdi_m_n m_n = {0};
 	u32 reg, temp;
+	u32 lvds_sync = 0;
 	int target_clock;
 
 	drm_vblank_pre_modeset(dev, pipe);
@@ -4755,6 +4756,22 @@ static int intel_crtc_mode_set(struct drm_crtc *crtc,
 			else
 				temp &= ~LVDS_ENABLE_DITHER;
 		}
+		if (adjusted_mode->flags & DRM_MODE_FLAG_NHSYNC)
+			lvds_sync |= LVDS_HSYNC_POLARITY;
+		if (adjusted_mode->flags & DRM_MODE_FLAG_NVSYNC)
+			lvds_sync |= LVDS_VSYNC_POLARITY;
+		if ((temp & (LVDS_HSYNC_POLARITY | LVDS_VSYNC_POLARITY))
+		    != lvds_sync) {
+			char flags[2] = "-+";
+			DRM_INFO("Changing LVDS panel from "
+				 "(%chsync, %cvsync) to (%chsync, %cvsync)\n",
+				 flags[!(temp & LVDS_HSYNC_POLARITY)],
+				 flags[!(temp & LVDS_VSYNC_POLARITY)],
+				 flags[!(lvds_sync & LVDS_HSYNC_POLARITY)],
+				 flags[!(lvds_sync & LVDS_VSYNC_POLARITY)]);
+			temp &= ~(LVDS_HSYNC_POLARITY | LVDS_VSYNC_POLARITY);
+			temp |= lvds_sync;
+		}
 		I915_WRITE(reg, temp);
 	}