The DSI PLL and HSDivider can be used to generate the pixel clock for LCD overlay manager, which then goes to DPI output. On the DPI output pin the voltage of the signal is shifted from the OMAP's internal minimal voltage to 1.8V range. The shifting is not instant, and the higher the clock frequency, the less time there is to shift the signal to nominal voltage. If the HSDivider's divider is greater than one and odd, the resulting pixel clock does not have 50% duty cycle. For example, with a divider of 3, the duty cycle is 33%. When combining high frequency (in the area of 140MHz+) and non-50% duty cycle, it has been observed the the shifter does not have enough time to shift the voltage enough, and this leads to bad signal which is rejected by monitors. As a workaround this patch makes the divider calculation skip all odd dividers when the required pixel clock is over 100MHz. Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxx> --- drivers/video/omap2/dss/dsi.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/video/omap2/dss/dsi.c b/drivers/video/omap2/dss/dsi.c index 7d0db2b..d0e35da 100644 --- a/drivers/video/omap2/dss/dsi.c +++ b/drivers/video/omap2/dss/dsi.c @@ -1386,6 +1386,11 @@ retry: cur.dsi_pll_hsdiv_dispc_clk = cur.clkin4ddr / cur.regm_dispc; + if (cur.regm_dispc > 1 && + cur.regm_dispc % 2 != 0 && + req_pck >= 1000000) + continue; + /* this will narrow down the search a bit, * but still give pixclocks below what was * requested */ -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
