drm/omapdrm: dispc: Refuse x-decimation above 4 for all but 8-bit formats

[uclinux-h8/linux.git] / drivers / gpu / drm / omapdrm / dss / dispc.c

diff --git a/drivers/gpu/drm/omapdrm/dss/dispc.c b/drivers/gpu/drm/omapdrm/dss/dispc.c
index 5554b72..d956e62 100644 (file)
--- 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;