drm/vc4: plane: Ensure fetch_count is sufficient for hw in SAND mode

It has been observed that under some situations the HVS stalls
totally when asked to apply a source crop to a P030/SAND128 image.

Investigation showed that it was always when the start offset
was on component 22 in the range 0-23. Increasing the fetch_count
by 1 under these conditions fixes the problem, so implement that
in the driver.

Signed-off-by: Dave Stevenson <[email protected]>

Author: 6by9

drivers/gpu/drm/vc4/vc4_plane.c

@@ -1983,6 +1983,9 @@ static int vc6_plane_mode_set(struct drm_plane *plane,
 
 				x_off = aligned * 32 + last_bits;
 				pix_per_tile = 96;
+
+				if (!i && last_bits == 22)
+					fetch_count++;
 			} else {
 				pix_per_tile = tile_width / fb->format->cpp[0];
 				x_off = (src_x % pix_per_tile) /