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OMAPDSS: DISPC: do only y decimation on OMAP3

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The current driver does both x and y decimation on OMAP3 DSS. Testing
shows that x decimation rarely works, leading to underflows.

The exact reason for this is unclear, as the underflows seem to happen
even with low pixel clock rates, and I would presume that if the DSS can
manage a display with 140MHz pixel clock, it could manage x decimation
with factor 2 with a low pixel clock (~30MHz).

So it is possible that there is a problem somewhere else, in memory
management, or DSS DMA, or similar. I have not found anything that would
help this.

So, to fix the downscaling scaling, this patch removes x decimation for
OMAP3. This will limit some of the more demanding downscaling scenarios,
but one could argue that using DSS to downscale such a large amount is
insane in the first place, as the produced image is rather bad quality.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
This commit is contained in:
Tomi Valkeinen 2015-04-10 12:48:38 +03:00
parent 3ce17b48da
commit 7059e3d8d8
1 changed files with 2 additions and 11 deletions
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13
drivers/video/fbdev/omap2/dss/dispc.c
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@ -2300,7 +2300,6 @@ static int dispc_ovl_calc_scaling_34xx(unsigned long pclk, unsigned long lclk,
{
int error;
u16 in_width, in_height;
int min_factor = min(*decim_x, *decim_y);
const int maxsinglelinewidth =
dss_feat_get_param_max(FEAT_PARAM_LINEWIDTH);
@ -2349,16 +2348,8 @@ again:
}
}
if (error) {
if (*decim_x == *decim_y) {
*decim_x = min_factor;
++*decim_y;
} else {
swap(*decim_x, *decim_y);
if (*decim_x < *decim_y)
++*decim_x;
}
}
if (error)
++*decim_y;
} while (*decim_x <= *x_predecim && *decim_y <= *y_predecim && error);
if (error) {