1 files changed, 19 insertions, 0 deletions

diff --git a/drivers/gpu/drm/omapdrm/dss/dispc.c b/drivers/gpu/drm/omapdrm/dss/dispc.c
index 5554b72cf56a..d956e6266368 100644
--- a/drivers/gpu/drm/omapdrm/dss/dispc.c
+++ b/drivers/gpu/drm/omapdrm/dss/dispc.c
@@ -2506,6 +2506,25 @@ static int dispc_ovl_calc_scaling_44xx(unsigned long pclk, unsigned long lclk,
                 return -EINVAL;
         }
 
+        if (*decim_x > 4 && color_mode != OMAP_DSS_COLOR_NV12) {
+                /*
+                 * Let's disable all scaling that requires horizontal
+                 * decimation with higher factor than 4, until we have
+                 * better estimates of what we can and can not
+                 * do. However, NV12 color format appears to work Ok
+                 * with all decimation factors.
+                 *
+                 * When decimating horizontally by more that 4 the dss
+                 * is not able to fetch the data in burst mode. When
+                 * this happens it is hard to tell if there enough
+                 * bandwidth. Despite what theory says this appears to
+                 * be true also for 16-bit color formats.
+                 */
+                DSSERR("Not enough bandwidth, too much downscaling (x-decimation factor %d > 4)", *decim_x);
+
+                return -EINVAL;
+        }
+
         *core_clk = dispc.feat->calc_core_clk(pclk, in_width, in_height,
                                 out_width, out_height, mem_to_mem);
         return 0;