sunxi: video: Add support for external DAC enable pin

The external DAC for VGA output might have either a power or reset
control pin that needs to be pulled up, as is the case on the
Hummingbird A31.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

board/sunxi/Kconfig

@@ -314,6 +314,14 @@ config VIDEO_VGA_VIA_LCD
 	LCD interface driving a VGA connector, such as found on the
 	Olimex A13 boards.
 
+config VIDEO_VGA_EXTERNAL_DAC_EN
+	string "LCD panel power enable pin"
+	depends on VIDEO_VGA_VIA_LCD
+	default ""
+	---help---
+	Set the enable pin for the external VGA DAC. This takes a string in the
+	format understood by sunxi_name_to_gpio, e.g. PH1 for pin 1 of port H.
+
 config VIDEO_LCD_MODE
 	string "LCD panel timing details"
 	depends on VIDEO

drivers/video/sunxi_display.c

@@ -813,6 +813,19 @@ static void sunxi_drc_init(void)
 #endif
 }
 
+#ifdef CONFIG_VIDEO_VGA_VIA_LCD
+static void sunxi_vga_external_dac_enable(void)
+{
+	int pin;
+
+	pin = sunxi_name_to_gpio(CONFIG_VIDEO_VGA_EXTERNAL_DAC_EN);
+	if (pin != -1) {
+		gpio_request(pin, "vga_enable");
+		gpio_direction_output(pin, 1);
+	}
+}
+#endif /* CONFIG_VIDEO_VGA_VIA_LCD */
+
 static void sunxi_engines_init(void)
 {
 	sunxi_composer_init();
@@ -860,6 +873,7 @@ static void sunxi_mode_set(const struct ctfb_res_modes *mode,
 		sunxi_lcdc_tcon0_mode_set(mode);
 		sunxi_composer_enable();
 		sunxi_lcdc_enable();
+		sunxi_vga_external_dac_enable();
 #endif
 		break;
 	}