Re: [PATCH v2 4/7] drm/bridge: Add RGB to VGA bridge support

Some boards have an entirely passive RGB to VGA bridge, based on either
DACs or resistor ladders.

Those might or might not have an i2c bus routed to the VGA connector in
order to access the screen EDIDs.

Add a bridge that doesn't do anything but expose the modes available on the
screen, either based on the EDIDs if available, or based on the XGA
standards.

Signed-off-by: Maxime Ripard <maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
---
 .../bindings/display/bridge/dumb-vga.txt           |  54 +++++
 drivers/gpu/drm/bridge/Kconfig                     |   6 +
 drivers/gpu/drm/bridge/Makefile                    |   1 +
 drivers/gpu/drm/bridge/dumb-vga.c                  | 232 +++++++++++++++++++++
 4 files changed, 293 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
 create mode 100644 drivers/gpu/drm/bridge/dumb-vga.c

diff --git a/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt
new file mode 100644
index 000000000000..0056ffa2b31d
--- /dev/null
+++ b/Documentation/devicetree/bindings/display/bridge/dumb-vga.txt

@@ -0,0 +1,54 @@
+Passive RGB to VGA bridge
+-------------------------
+
+This binding is aimed for entirely passive RGB to VGA bridges that do not
+require any configuration.
+
+Required properties:
+
+- compatible: Must be "dumb-vga-bridge"
+
+Required nodes:
+
+This device has two video ports. Their connections are modeled using the OF
+graph bindings specified in Documentation/devicetree/bindings/graph.txt.
+
+- Video port 0 for RGB input
+- Video port 1 for VGA output
+
+
+Example
+-------
+
+bridge {
+	compatible = "dumb-vga-bridge";
+	#address-cells = <1>;
+	#size-cells = <0>;
+
+	ports {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		port@0 {
+			#address-cells = <1>;
+			#size-cells = <0>;
+			reg = <0>;
+
+			vga_bridge_in: endpoint@0 {
+				reg = <0>;