[RFC PATCH 1/6] dt-bindings: display: add a device tree supplied boot logo

[Max Pedraza <maximpedraza@gmail.com>]

Embedded products frequently need a product specific boot logo. Today the
only way to get one is to replace one of the logo_*_clut224.ppm files in
the kernel source tree, which bakes the image into the kernel image: a
change of branding, or a second product sharing the same board support,
requires a separate kernel build.

Add a binding for a "linux,boot-logo-clut224" node, which carries the logo
in the same paletted format the built-in CLUT224 logos already use, plus a
few optional properties describing where on the screen it is drawn.

The palette size is derived from the length of the "clut" property rather
than spelled out separately, and "data" holds plain palette indices; the
32 entry offset the frame buffer layer reserves for the console is an
implementation detail and is applied by the kernel, not by the binding.

Signed-off-by: Max Pedraza <maximpedraza@gmail.com>
---
 .../display/linux,boot-logo-clut224.yaml      | 108 ++++++++++++++++++
 MAINTAINERS                                   |   1 +
 2 files changed, 109 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/linux,boot-logo-clut224.yaml

diff --git a/Documentation/devicetree/bindings/display/linux,boot-logo-clut224.yaml b/Documentation/devicetree/bindings/display/linux,boot-logo-clut224.yaml
new file mode 100644
index 000000000..10845378d
--- /dev/null
+++ b/Documentation/devicetree/bindings/display/linux,boot-logo-clut224.yaml
@@ -0,0 +1,108 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/linux,boot-logo-clut224.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Boot logo supplied by the device tree
+
+maintainers:
+  - Max Pedraza <maximpedraza@gmail.com>
+
+description: |
+  Embedded systems commonly need a product specific boot logo. Today the only
+  way to get one is to replace one of the logo_*_clut224.ppm files in the
+  kernel source tree, which means the image is baked into the kernel image and
+  a new kernel has to be built and deployed to change it.
+
+  This node lets the boot logo be described by the device tree instead, so that
+  a single kernel image can serve several products, or several revisions of the
+  same product, that only differ in branding.
+
+  The image is stored in the same paletted format the in-kernel CLUT224 logos
+  use: a palette of at most 224 RGB entries plus one palette index per pixel.
+
+properties:
+  compatible:
+    const: linux,boot-logo-clut224
+
+  width:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: Logo width in pixels.
+    minimum: 1
+    maximum: 65535
+
+  height:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: Logo height in pixels.
+    minimum: 1
+    maximum: 65535
+
+  clut:
+    $ref: /schemas/types.yaml#/definitions/uint8-array
+    description:
+      Colour lookup table, as consecutive red, green and blue bytes per entry.
+      The number of entries is derived from the property length and must not
+      exceed 224.
+    minItems: 3
+    maxItems: 672
+
+  data:
+    $ref: /schemas/types.yaml#/definitions/uint8-array
+    description:
+      One byte per pixel, left to right and top to bottom, each byte being an
+      index into the colour lookup table. The property length must be equal to
+      width multiplied by height.
+
+  logo-position:
+    $ref: /schemas/types.yaml#/definitions/uint32-array
+    description:
+      X and Y coordinates, in pixels, of the top left corner of the logo.
+      Defaults to the top left corner of the screen.
+    items:
+      - description: X coordinate
+      - description: Y coordinate
+
+  logo-offset:
+    $ref: /schemas/types.yaml#/definitions/int32-array
+    description:
+      X and Y displacement, in pixels, applied after the logo has been placed.
+      Mostly useful together with logo-centered.
+    items:
+      - description: X displacement
+      - description: Y displacement
+
+  logo-centered:
+    type: boolean
+    description:
+      Centre the logo on the screen, overriding logo-position.
+
+  logo-rotation:
+    $ref: /schemas/types.yaml#/definitions/string
+    description: Rotation applied to the logo before it is drawn.
+    enum: [none, cw, ccw, ud]
+    default: none
+
+required:
+  - compatible
+  - width
+  - height
+  - clut
+  - data
+
+additionalProperties: false
+
+examples:
+  - |
+    // A 4x2 logo using three colours, centred on the screen.
+    logo {
+        compatible = "linux,boot-logo-clut224";
+        width = <4>;
+        height = <2>;
+        clut = /bits/ 8 <0xff 0x00 0x00
+                         0x00 0xff 0x00
+                         0x00 0x00 0xff>;
+        data = /bits/ 8 <0x00 0x01 0x01 0x00
+                         0x02 0x00 0x00 0x02>;
+        logo-centered;
+    };
diff --git a/MAINTAINERS b/MAINTAINERS
index e08767323..3f0ede165 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -9951,6 +9951,7 @@ L:	dri-devel@lists.freedesktop.org
 S:	Maintained
 Q:	http://patchwork.kernel.org/project/linux-fbdev/list/
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/deller/linux-fbdev.git
+F:	Documentation/devicetree/bindings/display/linux,boot-logo-clut224.yaml
 F:	Documentation/fb/
 F:	drivers/video/
 F:	include/linux/fb.h
-- 
2.39.5