dt-bindings: display: convert display-timings to DT schema

Add display-timings.yaml - that references panel-timings.yaml.
display-timings.yaml will be used for display bindings
when they are converted to meta-schema format.

For now the old display-timing.txt points to the new
display-timings.yaml - and all users are left as-is.

v2:
  - Updated native-mode description

v3:
  - Simpler "^timing" pattern (Rob)
  - timing node is of type object (Rob)
  - added display-timings to panel-common.yaml
  - added yaml document terminator "..."
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>
Cc: devicetree@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20200216181513.28109-3-sam@ravnborg.org

Documentation/devicetree/bindings/display/panel/display-timing.txt

-display-timing bindings
-=======================
-
-display-timings node
---------------------
-
-required properties:
- - none
-
-optional properties:
- - native-mode: The native mode for the display, in case multiple modes are
-		provided. When omitted, assume the first node is the native.
-
-timing subnode
---------------
-
-required properties:
- - hactive, vactive: display resolution
- - hfront-porch, hback-porch, hsync-len: horizontal display timing parameters
-   in pixels
-   vfront-porch, vback-porch, vsync-len: vertical display timing parameters in
-   lines
- - clock-frequency: display clock in Hz
-
-optional properties:
- - hsync-active: hsync pulse is active low/high/ignored
- - vsync-active: vsync pulse is active low/high/ignored
- - de-active: data-enable pulse is active low/high/ignored
- - pixelclk-active: with
-			- active high = drive pixel data on rising edge/
-					sample data on falling edge
-			- active low  = drive pixel data on falling edge/
-					sample data on rising edge
-			- ignored     = ignored
- - syncclk-active: with
-			- active high = drive sync on rising edge/
-					sample sync on falling edge of pixel
-					clock
-			- active low  = drive sync on falling edge/
-					sample sync on rising edge of pixel
-					clock
-			- omitted     = same configuration as pixelclk-active
- - interlaced (bool): boolean to enable interlaced mode
- - doublescan (bool): boolean to enable doublescan mode
- - doubleclk (bool): boolean to enable doubleclock mode
-
-All the optional properties that are not bool follow the following logic:
-    <1>: high active
-    <0>: low active
-    omitted: not used on hardware
-
-There are different ways of describing the capabilities of a display. The
-devicetree representation corresponds to the one commonly found in datasheets
-for displays. If a display supports multiple signal timings, the native-mode
-can be specified.
-
-The parameters are defined as:
-
-  +----------+-------------------------------------+----------+-------+
-  |          |        ^                            |          |       |
-  |          |        |vback_porch                 |          |       |
-  |          |        v                            |          |       |
-  +----------#######################################----------+-------+
-  |          #        ^                            #          |       |
-  |          #        |                            #          |       |
-  |  hback   #        |                            #  hfront  | hsync |
-  |   porch  #        |       hactive              #  porch   |  len  |
-  |<-------->#<-------+--------------------------->#<-------->|<----->|
-  |          #        |                            #          |       |
-  |          #        |vactive                     #          |       |
-  |          #        |                            #          |       |
-  |          #        v                            #          |       |
-  +----------#######################################----------+-------+
-  |          |        ^                            |          |       |
-  |          |        |vfront_porch                |          |       |
-  |          |        v                            |          |       |
-  +----------+-------------------------------------+----------+-------+
-  |          |        ^                            |          |       |
-  |          |        |vsync_len                   |          |       |
-  |          |        v                            |          |       |
-  +----------+-------------------------------------+----------+-------+
-
-Note: In addition to being used as subnode(s) of display-timings, the timing
-      subnode may also be used on its own. This is appropriate if only one mode
-      need be conveyed. In this case, the node should be named 'panel-timing'.
-
-
-Example:
-
-	display-timings {
-		native-mode = <&timing0>;
-		timing0: 1080p24 {
-			/* 1920x1080p24 */
-			clock-frequency = <52000000>;
-			hactive = <1920>;
-			vactive = <1080>;
-			hfront-porch = <25>;
-			hback-porch = <25>;
-			hsync-len = <25>;
-			vback-porch = <2>;
-			vfront-porch = <2>;
-			vsync-len = <2>;
-			hsync-active = <1>;
-		};
-	};
-
-Every required property also supports the use of ranges, so the commonly used
-datasheet description with minimum, typical and maximum values can be used.
-
-Example:
-
-	timing1: timing {
-		/* 1920x1080p24 */
-		clock-frequency = <148500000>;
-		hactive = <1920>;
-		vactive = <1080>;
-		hsync-len = <0 44 60>;
-		hfront-porch = <80 88 95>;
-		hback-porch = <100 148 160>;
-		vfront-porch = <0 4 6>;
-		vback-porch = <0 36 50>;
-		vsync-len = <0 5 6>;
-	};
+See display-timings.yaml in this directory.

Documentation/devicetree/bindings/display/panel/display-timings.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/panel/display-timings.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: display timing bindings
+
+maintainers:
+  - Thierry Reding <thierry.reding@gmail.com>
+  - Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
+  - Sam Ravnborg <sam@ravnborg.org>
+
+description: |
+  A display panel may be able to handle several display timings,
+  with different resolutions.
+  The display-timings node makes it possible to specify the timing
+  and to specify the timing that is native for the display.
+
+properties:
+  $nodename:
+    const: display-timings
+
+  native-mode:
+    $ref: /schemas/types.yaml#/definitions/phandle
+    description: |
+      The default display timing is the one specified as native-mode.
+      If no native-mode is specified then the first node is assumed the
+      native mode.
+
+patternProperties:
+  "^timing":
+    type: object
+    allOf:
+      - $ref: panel-timing.yaml#
+
+additionalProperties: false
+
+examples:
+  - |+
+
+    /*
+     * Example that specifies panel timing using minimum, typical,
+     * maximum values as commonly used in datasheet description.
+     * timing1 is the native-mode.
+     */
+    display-timings {
+        native-mode = <&timing1>;
+        timing0 {
+            /* 1920x1080p24 */
+            clock-frequency = <148500000>;
+            hactive = <1920>;
+            vactive = <1080>;
+            hsync-len = <0 44 60>;
+            hfront-porch = <80 88 95>;
+            hback-porch = <100 148 160>;
+            vfront-porch = <0 4 6>;
+            vback-porch = <0 36 50>;
+            vsync-len = <0 5 6>;
+        };
+        timing1 {
+            /* 1920x1080p24 */
+            clock-frequency = <52000000>;
+            hactive = <1920>;
+            vactive = <1080>;
+            hfront-porch = <25>;
+            hback-porch = <25>;
+            hsync-len = <0 25 25>;
+            vback-porch = <2>;
+            vfront-porch = <2>;
+            vsync-len = <2>;
+            hsync-active = <1>;
+            pixelclk-active = <1>;
+        };
+    };
+
+...

Documentation/devicetree/bindings/display/panel/panel-common.yaml

@@ -61,6 +61,14 @@ properties:
     allOf:
       - $ref: panel-timing.yaml#
 
+  display-timings:
+    description:
+      Some display panels supports several resolutions with different timing.
+      The display-timings bindings supports specifying several timings and
+      optional specify which is the native mode.
+    allOf:
+      - $ref: display-timings.yaml#
+
   # Connectivity
   port:
     type: object