OMAPDSS: DISPC: Configure writeback FIFOs

Extend the DISPC fifo functions to also configure the writeback FIFO thresholds.

The most optimal configuration for writeback is to push out data to the
interconnect the moment writeback pushes enough pixels in the FIFO to form a
burst. This reduces the chance of writeback overflowing it's FIFO.
Signed-off-by: Archit Taneja <archit@ti.com>

drivers/video/omap2/dss/dispc.c

@@ -993,7 +993,7 @@ void dispc_wb_set_channel_in(enum dss_writeback_channel channel)
 static void dispc_ovl_set_burst_size(enum omap_plane plane,
 		enum omap_burst_size burst_size)
 {
-	static const unsigned shifts[] = { 6, 14, 14, 14, };
+	static const unsigned shifts[] = { 6, 14, 14, 14, 14, };
 	int shift;
 
 	shift = shifts[plane];
@@ -1225,6 +1225,14 @@ void dispc_ovl_compute_fifo_thresholds(enum omap_plane plane,
 	if (manual_update && dss_has_feature(FEAT_OMAP3_DSI_FIFO_BUG)) {
 		*fifo_low = ovl_fifo_size - burst_size * 2;
 		*fifo_high = total_fifo_size - burst_size;
+	} else if (plane == OMAP_DSS_WB) {
+		/*
+		 * Most optimal configuration for writeback is to push out data
+		 * to the interconnect the moment writeback pushes enough pixels
+		 * in the FIFO to form a burst
+		 */
+		*fifo_low = 0;
+		*fifo_high = burst_size;
 	} else {
 		*fifo_low = ovl_fifo_size - burst_size;
 		*fifo_high = total_fifo_size - buf_unit;