From: Mikulas Patocka <mpatocka@xxxxxxxxxx> Date: Fri, 17 Aug 2018 15:19:37 -0400 (EDT) > On Sun Ultra 5, it happens that the dot clock is not set up properly for > some videomodes. For example, if we set the videomode "r1024x768x60" in > the firmware, Linux would incorrectly set a videomode with refresh rate > 180Hz when booting (suprisingly, my LCD monitor can display it, although > display quality is very low). > > The reason is this: Older mach64 cards set the divider in the register > VCLK_POST_DIV. The register has four 2-bit fields (the field that is > actually used is specified in the lowest two bits of the register > CLOCK_CNTL). The 2 bits select divider "1, 2, 4, 8". On newer mach64 cards, > there's another bit added - the top four bits of PLL_EXT_CNTL extend the > divider selection, so we have possible dividers "1, 2, 4, 8, 3, 5, 6, 12". > The Linux driver clears the top four bits of PLL_EXT_CNTL and never sets > them, so it can work regardless if the card supports them. However, the > sparc64 firmware may set these extended dividers during boot - and the > mach64 driver detects incorrect dot clock in this case. > > This patch makes the driver read the additional divider bit from > PLL_EXT_CNTL and calculate the initial refresh rate properly. > > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx Acked-by: David S. Miller <davem@xxxxxxxxxxxxx> _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
