dt-bindings: display: add panel-timing.yaml

Add meta-schema variant of panel-timing and
reference it from panel-common.yaml.

Part of this came form other files with other
licenses - original commits:

commit cc3f414c ("video: add of helper for display timings/videomode")
commit 86f46565 ("dt-bindings: display: display-timing: Add property to configure sync drive edge")
commit 9cad9c95 ("Documentation: DocBook DRM framework documentation")

The original authors acked the license change to:
(GPL-2.0-only OR BSD-2-Clause)

v2:
  - Got OK from original authors for re-license
    Huge thanks for the quick replies!
  - Typo fixes (Oleksandr)
  - Drop -array variant when not needed (Maxime)
  - Replace oneOf:... with enum (Maxime)
  - Drop type from clock-frequency (Rob)
  - Drop "|" when not needed (Rob)

v3:
  - Added comment to acks that are only for the license change
  - Add yaml document terminator "..."
  - Updated description (removed reference to native-mode)
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> [license change]
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com> [license change]
Acked-by: Steffen Trumtrar <s.trumtrar@pengutronix.de> [license change]
Acked-by: Philipp Zabel <p.zabel@pengutronix.de> [license change]
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: devicetree@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20200216181513.28109-2-sam@ravnborg.org

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

@@ -54,13 +54,12 @@ properties:
 
   # Display Timings
   panel-timing:
-    type: object
     description:
       Most display panels are restricted to a single resolution and
       require specific display timings. The panel-timing subnode expresses those
-      timings as specified in the timing subnode section of the display timing
-      bindings defined in
-      Documentation/devicetree/bindings/display/panel/display-timing.txt.
+      timings.
+    allOf:
+      - $ref: panel-timing.yaml#
 
   # Connectivity
   port:

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

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/panel/panel-timing.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: panel timing bindings
+
+maintainers:
+  - Thierry Reding <thierry.reding@gmail.com>
+  - Sam Ravnborg <sam@ravnborg.org>
+
+description: |
+  There are different ways of describing the timing data of a panel. The
+  devicetree representation corresponds to the one commonly found in datasheets
+  for panels.
+
+  The parameters are defined as seen in the following illustration.
+
+  +----------+-------------------------------------+----------+-------+
+  |          |        ^                            |          |       |
+  |          |        |vback_porch                 |          |       |
+  |          |        v                            |          |       |
+  +----------#######################################----------+-------+
+  |          #        ^                            #          |       |
+  |          #        |                            #          |       |
+  |  hback   #        |                            #  hfront  | hsync |
+  |   porch  #        |       hactive              #  porch   |  len  |
+  |<-------->#<-------+--------------------------->#<-------->|<----->|
+  |          #        |                            #          |       |
+  |          #        |vactive                     #          |       |
+  |          #        |                            #          |       |
+  |          #        v                            #          |       |
+  +----------#######################################----------+-------+
+  |          |        ^                            |          |       |
+  |          |        |vfront_porch                |          |       |
+  |          |        v                            |          |       |
+  +----------+-------------------------------------+----------+-------+
+  |          |        ^                            |          |       |
+  |          |        |vsync_len                   |          |       |
+  |          |        v                            |          |       |
+  +----------+-------------------------------------+----------+-------+
+
+
+  The following is the panel timings shown with time on the x-axis.
+  This matches the timing diagrams often found in data sheets.
+
+              Active                 Front           Sync           Back
+              Region                 Porch                          Porch
+  <-----------------------><----------------><-------------><-------------->
+    //////////////////////|
+   ////////////////////// |
+  //////////////////////  |..................               ................
+                                             _______________
+
+  Timing can be specified either as a typical value or as a tuple
+  of min, typ, max values.
+
+properties:
+
+  clock-frequency:
+   description: Panel clock in Hz
+
+  hactive:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: Horizontal panel resolution in pixels
+
+  vactive:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: Vertical panel resolution in pixels
+
+  hfront-porch:
+    description: Horizontal front porch panel timing
+    oneOf:
+      - allOf:
+        - $ref: /schemas/types.yaml#/definitions/uint32
+        - maxItems: 1
+          items:
+            description: typical number of pixels
+      - allOf:
+        - $ref: /schemas/types.yaml#/definitions/uint32-array
+        - minItems: 3
+          maxItems: 3
+          items:
+            description: min, typ, max number of pixels
+
+  hback-porch:
+    description: Horizontal back porch timing
+    oneOf:
+      - allOf:
+        - $ref: /schemas/types.yaml#/definitions/uint32
+        - maxItems: 1
+          items:
+            description: typical number of pixels
+      - allOf:
+        - $ref: /schemas/types.yaml#/definitions/uint32-array
+        - minItems: 3
+          maxItems: 3
+          items:
+            description: min, typ, max number of pixels
+
+  hsync-len:
+    description: Horizontal sync length panel timing
+    oneOf:
+      - allOf:
+        - $ref: /schemas/types.yaml#/definitions/uint32
+        - maxItems: 1
+          items:
+            description: typical number of pixels
+      - allOf:
+        - $ref: /schemas/types.yaml#/definitions/uint32-array
+        - minItems: 3
+          maxItems: 3
+          items:
+            description: min, typ, max number of pixels
+
+  vfront-porch:
+    description: Vertical front porch panel timing
+    oneOf:
+      - allOf:
+        - $ref: /schemas/types.yaml#/definitions/uint32
+        - maxItems: 1
+          items:
+            description: typical number of lines
+      - allOf:
+        - $ref: /schemas/types.yaml#/definitions/uint32-array
+        - minItems: 3
+          maxItems: 3
+          items:
+            description: min, typ, max number of lines
+
+  vback-porch:
+    description: Vertical back porch panel timing
+    oneOf:
+      - allOf:
+        - $ref: /schemas/types.yaml#/definitions/uint32
+        - maxItems: 1
+          items:
+            description: typical number of lines
+      - allOf:
+        - $ref: /schemas/types.yaml#/definitions/uint32-array
+        - minItems: 3
+          maxItems: 3
+          items:
+            description: min, typ, max number of lines
+
+  vsync-len:
+    description: Vertical sync length panel timing
+    oneOf:
+      - allOf:
+        - $ref: /schemas/types.yaml#/definitions/uint32
+        - maxItems: 1
+          items:
+            description: typical number of lines
+      - allOf:
+        - $ref: /schemas/types.yaml#/definitions/uint32-array
+        - minItems: 3
+          maxItems: 3
+          items:
+            description: min, typ, max number of lines
+
+  hsync-active:
+    description: |
+      Horizontal sync pulse.
+      0 selects active low, 1 selects active high.
+      If omitted then it is not used by the hardware
+    enum: [0, 1]
+
+  vsync-active:
+    description: |
+      Vertical sync pulse.
+      0 selects active low, 1 selects active high.
+      If omitted then it is not used by the hardware
+    enum: [0, 1]
+
+  de-active:
+    description: |
+      Data enable.
+      0 selects active low, 1 selects active high.
+      If omitted then it is not used by the hardware
+    enum: [0, 1]
+
+  pixelclk-active:
+    description: |
+      Data driving on rising or falling edge.
+      Use 0 to drive pixel data on falling edge and
+      sample data on rising edge.
+      Use 1 to drive pixel data on rising edge and
+      sample data on falling edge
+    enum: [0, 1]
+
+  syncclk-active:
+    description: |
+      Drive sync on rising or sample sync on falling edge.
+      If not specified then the setup is as specified by pixelclk-active.
+      Use 0 to drive sync on falling edge and
+      sample sync on rising edge of pixel clock.
+      Use 1 to drive sync on rising edge and
+      sample sync on falling edge of pixel clock
+    enum: [0, 1]
+
+  interlaced:
+    type: boolean
+    description: Enable interlaced mode
+
+  doublescan:
+    type: boolean
+    description: Enable double scan mode
+
+  doubleclk:
+    type: boolean
+    description: Enable double clock mode
+
+required:
+ - clock-frequency
+ - hactive
+ - vactive
+ - hfront-porch
+ - hback-porch
+ - hsync-len
+ - vfront-porch
+ - vback-porch
+ - vsync-len
+
+additionalProperties: false
+
+...