drm/tilcdc fixup mode to workaround sync for tda998x

Add a fixup function that will flip the hsync priority and
add a hskew value that is used to shift the tda998x to the
right by a variable number of pixels depending on the mode.
This works around an issue with the sync timings that tilcdc
is outputing.

Signed-off-by: Darren Etheridge <detheridge@ti.com>
Tested-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/tilcdc/tilcdc_crtc.c

@@ -379,7 +379,12 @@ static int tilcdc_crtc_mode_set(struct drm_crtc *crtc,
 	else
 		tilcdc_clear(dev, LCDC_RASTER_TIMING_2_REG, LCDC_SYNC_EDGE);
 
-	if (mode->flags & DRM_MODE_FLAG_NHSYNC)
+	/*
+	 * use value from adjusted_mode here as this might have been
+	 * changed as part of the fixup for slave encoders to solve the
+	 * issue where tilcdc timings are not VESA compliant
+	 */
+	if (adjusted_mode->flags & DRM_MODE_FLAG_NHSYNC)
 		tilcdc_set(dev, LCDC_RASTER_TIMING_2_REG, LCDC_INVERT_HSYNC);
 	else
 		tilcdc_clear(dev, LCDC_RASTER_TIMING_2_REG, LCDC_INVERT_HSYNC);

drivers/gpu/drm/tilcdc/tilcdc_slave.c

@@ -73,13 +73,38 @@ static void slave_encoder_prepare(struct drm_encoder *encoder)
 	tilcdc_crtc_set_panel_info(encoder->crtc, &slave_info);
 }
 
+static bool slave_encoder_fixup(struct drm_encoder *encoder,
+		const struct drm_display_mode *mode,
+		struct drm_display_mode *adjusted_mode)
+{
+	/*
+	 * tilcdc does not generate VESA-complient sync but aligns
+	 * VS on the second edge of HS instead of first edge.
+	 * We use adjusted_mode, to fixup sync by aligning both rising
+	 * edges and add HSKEW offset to let the slave encoder fix it up.
+	 */
+	adjusted_mode->hskew = mode->hsync_end - mode->hsync_start;
+	adjusted_mode->flags |= DRM_MODE_FLAG_HSKEW;
+
+	if (mode->flags & DRM_MODE_FLAG_NHSYNC) {
+		adjusted_mode->flags |= DRM_MODE_FLAG_PHSYNC;
+		adjusted_mode->flags &= ~DRM_MODE_FLAG_NHSYNC;
+	} else {
+		adjusted_mode->flags |= DRM_MODE_FLAG_NHSYNC;
+		adjusted_mode->flags &= ~DRM_MODE_FLAG_PHSYNC;
+	}
+
+	return drm_i2c_encoder_mode_fixup(encoder, mode, adjusted_mode);
+}
+
+
 static const struct drm_encoder_funcs slave_encoder_funcs = {
 		.destroy        = slave_encoder_destroy,
 };
 
 static const struct drm_encoder_helper_funcs slave_encoder_helper_funcs = {
 		.dpms           = drm_i2c_encoder_dpms,
-		.mode_fixup     = drm_i2c_encoder_mode_fixup,
+		.mode_fixup     = slave_encoder_fixup,
 		.prepare        = slave_encoder_prepare,
 		.commit         = drm_i2c_encoder_commit,
 		.mode_set       = drm_i2c_encoder_mode_set,