Commit 7059e3d8 authored Apr 10, 2015 by Tomi Valkeinen

OMAPDSS: DISPC: do only y decimation on OMAP3

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>

parent 3ce17b48

drivers/video/fbdev/omap2/dss/dispc.c

+2 −11

Original line number	Diff line number	Diff line
		@@ -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 @@ static int dispc_ovl_calc_scaling_34xx(unsigned long pclk, unsigned long lclk,
		}
		}

		if (error) {
		if (decim_x == decim_y) {
		*decim_x = min_factor;
		if (error)
		++*decim_y;
		} else {
		swap(decim_x, decim_y);
		if (decim_x < decim_y)
		++*decim_x;
		}
		}
		} while (decim_x <= x_predecim && decim_y <= y_predecim && error);

		if (error) {