From fb75d972eaf5c887ada28e73d3e84d52931d4cb0 Mon Sep 17 00:00:00 2001 From: Hans de Goede Date: Sun, 25 Jan 2015 15:33:07 +0100 Subject: sunxi: video: Force h/vsync active high when using ext. vga dac on some boards On both my A13-OLinuxIno and my A13-OLinuxIno-Micro, the vga output gives an unstable image when active low v or hsync is used. The problem seems to be specific to the OLinuxIno A13 (normal & micro) boards. I've just looked up the schematics and they use an opendrain driver for the vga sync lines, and with sync pulses it is the logical high->low edge of the pulse which counts for the timing, which with an active low sync is being driven by the pull-up, and that simply seems to not drive it hard enough to get a stable image. So force v and hsync active high on these boards. independent of what the modeline says. This fixes the unstable image. Signed-off-by: Hans de Goede Acked-by: Ian Campbell --- board/sunxi/Kconfig | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'board') diff --git a/board/sunxi/Kconfig b/board/sunxi/Kconfig index 4b31dcc..adbd2b5 100644 --- a/board/sunxi/Kconfig +++ b/board/sunxi/Kconfig @@ -185,6 +185,16 @@ config VIDEO_VGA_VIA_LCD LCD interface driving a VGA connector, such as found on the Olimex A13 boards. +config VIDEO_VGA_VIA_LCD_FORCE_SYNC_ACTIVE_HIGH + boolean "Force sync active high for VGA via LCD controller support" + depends on VIDEO_VGA_VIA_LCD + default n + ---help--- + Say Y here if you've a board which uses opendrain drivers for the vga + hsync and vsync signals. Opendrain drivers cannot generate steep enough + positive edges for a stable video output, so on boards with opendrain + drivers the sync signals must always be active high. + config VIDEO_VGA_EXTERNAL_DAC_EN string "LCD panel power enable pin" depends on VIDEO_VGA_VIA_LCD -- cgit v1.1