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authorHans de Goede <hdegoede@redhat.com>2015-01-25 15:33:07 +0100
committerHans de Goede <hdegoede@redhat.com>2015-02-02 13:57:16 +0100
commitfb75d972eaf5c887ada28e73d3e84d52931d4cb0 (patch)
tree1bd562e1ddadc7242ca3027a898c0f7461bd6501 /board
parent8d0df9be927eff1be9aef29aa995f6b54900962e (diff)
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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>
Diffstat (limited to 'board')
-rw-r--r--board/sunxi/Kconfig10
1 files changed, 10 insertions, 0 deletions
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