drm/i2c: tda998x: prepare for broken sync workaround

Some LCD controller cannot provide valid VESA style sync, i.e. coincident
HS/VS edges. First, this patch adds hskew passed from the adjusted_mode to
reference pixel calculation to allow those controllers to add an offset
relative to the expected reference pixel.
Signed-off-by: Darren Etheridge <detheridge@ti.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Tested-by: Russell King <rmk_kernel@arm.linux.org.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/i2c/tda998x_drv.c

@@ -782,6 +782,14 @@ tda998x_encoder_mode_set(struct drm_encoder *encoder,
 	de_pix_s     = mode->htotal - mode->hdisplay;
 	ref_pix      = 3 + hs_pix_s;
 
+	/*
+	 * Attached LCD controllers may generate broken sync. Allow
+	 * those to adjust the position of the rising VS edge by adding
+	 * HSKEW to ref_pix.
+	 */
+	if (adjusted_mode->flags & DRM_MODE_FLAG_HSKEW)
+		ref_pix += adjusted_mode->hskew;
+
 	if ((mode->flags & DRM_MODE_FLAG_INTERLACE) == 0) {
 		ref_line     = 1 + mode->vsync_start - mode->vdisplay;
 		vwin1_line_s = mode->vtotal - mode->vdisplay - 1;