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>

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

configs/A13-OLinuXinoM_defconfig

@@ -4,6 +4,7 @@ CONFIG_FDTFILE="sun5i-a13-olinuxino-micro.dtb"
 CONFIG_USB1_VBUS_PIN="PG11"
 CONFIG_VIDEO_HDMI=n
 CONFIG_VIDEO_VGA_VIA_LCD=y
+CONFIG_VIDEO_VGA_VIA_LCD_FORCE_SYNC_ACTIVE_HIGH=y
 # For use with the Olimex 7" LCD module, adjust timings for other displays
 # Set video-mode=sunxi:800x600-24@60,monitor=lcd in the env. to enable
 CONFIG_VIDEO_LCD_MODE="x:800,y:480,depth:18,pclk_khz:33000,le:16,ri:209,up:22,lo:22,hs:30,vs:1,sync:3,vmode:0"

configs/A13-OLinuXino_defconfig

@@ -4,6 +4,7 @@ CONFIG_FDTFILE="sun5i-a13-olinuxino.dtb"
 CONFIG_USB1_VBUS_PIN="PG11"
 CONFIG_VIDEO_HDMI=n
 CONFIG_VIDEO_VGA_VIA_LCD=y
+CONFIG_VIDEO_VGA_VIA_LCD_FORCE_SYNC_ACTIVE_HIGH=y
 # For use with the Olimex 7" LCD module, adjust timings for other displays
 # Set video-mode=sunxi:800x600-24@60,monitor=lcd in the env. to enable
 CONFIG_VIDEO_LCD_MODE="x:800,y:480,depth:18,pclk_khz:33000,le:16,ri:209,up:22,lo:22,hs:30,vs:1,sync:3,vmode:0"

drivers/video/sunxi_display.c

@@ -645,7 +645,8 @@ static int sunxi_lcdc_get_clk_delay(const struct ctfb_res_modes *mode)
 	return (delay > 30) ? 30 : delay;
 }
 
-static void sunxi_lcdc_tcon0_mode_set(const struct ctfb_res_modes *mode)
+static void sunxi_lcdc_tcon0_mode_set(const struct ctfb_res_modes *mode,
+				      bool for_ext_vga_dac)
 {
 	struct sunxi_lcdc_reg * const lcdc =
 		(struct sunxi_lcdc_reg *)SUNXI_LCD0_BASE;
@@ -719,6 +720,11 @@ static void sunxi_lcdc_tcon0_mode_set(const struct ctfb_res_modes *mode)
 		val |= SUNXI_LCDC_TCON_HSYNC_MASK;
 	if (!(mode->sync & FB_SYNC_VERT_HIGH_ACT))
 		val |= SUNXI_LCDC_TCON_VSYNC_MASK;
+
+#ifdef CONFIG_VIDEO_VGA_VIA_LCD_FORCE_SYNC_ACTIVE_HIGH
+	if (for_ext_vga_dac)
+		val = 0;
+#endif
 	writel(val, &lcdc->tcon0_io_polarity);
 
 	writel(0, &lcdc->tcon0_io_tristate);
@@ -1015,7 +1021,7 @@ static void sunxi_mode_set(const struct ctfb_res_modes *mode,
 			hitachi_tx18d42vm_init();
 		}
 		sunxi_composer_mode_set(mode, address);
-		sunxi_lcdc_tcon0_mode_set(mode);
+		sunxi_lcdc_tcon0_mode_set(mode, false);
 		sunxi_composer_enable();
 		sunxi_lcdc_enable();
 #ifdef CONFIG_VIDEO_LCD_SSD2828
@@ -1033,7 +1039,7 @@ static void sunxi_mode_set(const struct ctfb_res_modes *mode,
 		sunxi_vga_enable();
 #elif defined CONFIG_VIDEO_VGA_VIA_LCD
 		sunxi_composer_mode_set(mode, address);
-		sunxi_lcdc_tcon0_mode_set(mode);
+		sunxi_lcdc_tcon0_mode_set(mode, true);
 		sunxi_composer_enable();
 		sunxi_lcdc_enable();
 		sunxi_vga_external_dac_enable();