[PATCH] dt-bindings: non-dt-devices: document ltr,ltrf216a used via ACPI PRP0001

[Krzysztof Kozlowski]

There is a device in the wild with non-updatable firmware coming with
ACPI tables with rejected "ltr,ltrf216a" compatible.  Linux kernel still
supports this device via ACPI PRP0001, however the compatible was never
accepted to bindings.  Lack of bindings causes checkpatch.pl warning
about undocumented compatible.

Add a schema for such ACPI PRP0001 devices purely to satisfy
checkpatch.pl and document consensus: ltr,ltrf216a compatible is allowed
only via ACPI PRP0001, but not bindings.

Link: https://lore.kernel.org/all/20240705095047.90558-1-marex@xxxxxxx/
Link: https://lore.kernel.org/lkml/20220731173446.7400bfa8@jic23-huawei/T/#me55be502302d70424a85368c2645c89f860b7b40
Cc: Marek Vasut <marex@xxxxxxx>
Cc: Jonathan Cameron <jic23@xxxxxxxxxx>
Cc: Sebastian Reichel <sebastian.reichel@xxxxxxxxxxxxx>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
---
 .../devicetree/bindings/non-dt-devices.yaml   | 35 +++++++++++++++++++
 1 file changed, 35 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/non-dt-devices.yaml

diff --git a/Documentation/devicetree/bindings/non-dt-devices.yaml b/Documentation/devicetree/bindings/non-dt-devices.yaml
new file mode 100644
index 000000000000..206334693c7b
--- /dev/null
+++ b/Documentation/devicetree/bindings/non-dt-devices.yaml
@@ -0,0 +1,35 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/non-dt-devices.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Non-devicetree Devices - Exception List
+
+maintainers:
+  - Rob Herring <robh@xxxxxxxxxx>
+
+description:
+  Some devices using ACPI with non-updatable firmware/ACPI tables use
+  incorrect Devicetree compatibles via ACPI PRP0001.  Developers want to
+  support these devices, thus use such compatibles in Linux drivers, however
+  usage of these within Devicetree sources was rejected.
+
+  Following list of devices is an incomplete schema with a goal to pass Linux
+  kernel scripts/checkpatch.pl checks about undocumented compatibles but also
+  reject any DTS file using such un-approved compatible.
+
+  Usage of any of following compatibles is not allowed in Devicetree sources,
+  even if they come from immutable firmware.  New entries can be added
+  only on the basis of non-updatable ACPI firmware on the device.
+
+properties:
+  compatible:
+    enum:
+      - ltr,ltrf216a
+
+required:
+  - compatible
+  - broken-usage-of-incorrect-compatible
+
+additionalProperties: false
-- 
2.43.0