On OMAP3/AM43xx some scaling factors cause underflows/synclosts. After
studying this, I found that sometimes the driver uses three-tap scaling
with downscaling factor smaller than x0.5. This causes issues, as x0.5
is the limit for three-tap scaling.
The driver has FEAT_PARAM_DOWNSCALE parameter, but that seems to be for
five-tap scaling, which allows scaling down to x0.25.
This patch adds checks for both horizontal and vertical scaling. For
horizontal the HW always uses 5 taps, so the limit is x0.25.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
---
drivers/video/fbdev/omap2/dss/dispc.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/drivers/video/fbdev/omap2/dss/dispc.c b/drivers/video/fbdev/omap2/dss/dispc.c
index cc61513afdb4..ddce8fcfc5c1 100644
--- a/drivers/video/fbdev/omap2/dss/dispc.c
+++ b/drivers/video/fbdev/omap2/dss/dispc.c
@@ -2326,6 +2326,21 @@ again:
error = (error || in_width > maxsinglelinewidth * 2 ||
(in_width > maxsinglelinewidth && *five_taps) ||
!*core_clk || *core_clk > dispc_core_clk_rate());
+
+ if (!error) {
+ /* verify that we're inside the limits of scaler */
+ if (in_width / 4 > out_width)
+ error = 1;
+
+ if (*five_taps) {
+ if (in_height / 4 > out_height)
+ error = 1;
+ } else {
+ if (in_height / 2 > out_height)
+ error = 1;
+ }
+ }
+
if (error) {
if (*decim_x == *decim_y) {
*decim_x = min_factor;
--
2.1.4
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