drm/tilcdc: Add blue-and-red-crossed devicetree property

Add "blue-and-red-wiring"-device tree property and update devicetree
binding document.

The red and blue components are reversed between 24 and 16 bit modes
on am335x LCDC output pins. To get 24 RGB format the red and blue
wires has to be crossed and this in turn causes 16 colors output to be
in BGR format. With straight wiring the 16 color is RGB and 24 bit is
BGR.

The new property describes whether the red and blue wires are crossed
or not. If the property is not present or its value is not recognized
the legacy mode is assumed. The legacy configuration supports RGB565,
RGB888 and XRGB8888 formats. However, depending on wiring, the red and
blue colors are swapped in either 16 or 24-bit color modes.

For more details see section 3.1.1 in AM335x Silicon Errata:
http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=sprz360

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/display/tilcdc/tilcdc.txt b/Documentation/devicetree/bindings/display/tilcdc/tilcdc.txt
index 6efa4c55d118..a5007aa437f3 100644
--- a/Documentation/devicetree/bindings/display/tilcdc/tilcdc.txt
+++ b/Documentation/devicetree/bindings/display/tilcdc/tilcdc.txt
@@ -17,6 +17,18 @@ Optional properties:
    the lcd controller.
  - max-pixelclock: The maximum pixel clock that can be supported
    by the lcd controller in KHz.
+ - blue-and-red-wiring: Recognized values "default", "straight" or
+   "crossed". This property deals with the LCDC revision 2 (found on
+   AM335x) color errata [1].
+    - "straight" indicates normal wiring that supports RGB565,
+      BGR888, and XBGR8888 color formats.
+    - "crossed" indicates wiring that has blue and red wires
+      crossed. This setup supports BGR565, RGB888 and XRGB8888
+      formats.
+    - If the property is not present or its value is not recognized
+      the legacy mode is assumed. This configuration supports RGB565,
+      RGB888 and XRGB8888 formats. However, depending on wiring, the red
+      and blue colors are swapped in either 16 or 24-bit color modes.
 
 Optional nodes:
 
@@ -28,6 +40,14 @@ Optional nodes:
    Documentation/devicetree/bindings/display/tilcdc/tfp410.txt for connecting
    tfp410 DVI encoder or lcd panel to lcdc
 
+[1] There is an errata about AM335x color wiring. For 16-bit color mode
+    the wires work as they should (LCD_DATA[0:4] is for Blue[3:7]),
+    but for 24 bit color modes the wiring of blue and red components is
+    crossed and LCD_DATA[0:4] is for Red[3:7] and LCD_DATA[11:15] is
+    for Blue[3-7]. For more details see section 3.1.1 in AM335x
+    Silicon Errata:
+    http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=sprz360
+
 Example:
 
 	fb: fb@4830e000 {
@@ -37,6 +57,8 @@ Example:
 		interrupts = <36>;
 		ti,hwmods = "lcdc";
 
+		blue-and-red-wiring = "crossed";
+
 		port {
 			lcdc_0: endpoint@0 {
 				remote-endpoint = <&hdmi_0>;