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 <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>
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 @@
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