dt-bindings: incomplete-devices: document devices without bindings

There are devices in the wild with non-updatable firmware coming with
ACPI tables with rejected compatibles, e.g. "ltr,ltrf216a".  Linux
kernel still supports this device via ACPI PRP0001, however the
compatible was never accepted to bindings.

There are also several early PowerPC or SPARC platforms using
compatibles for their OpenFirmware, but without in-tree DTS.  Often the
legacy compatible is not correct in terms of current Devicetree
specification, e.g. missing vendor prefix.

Finally there are also Linux-specific tools and test code with
compatibles.

Add a schema covering above cases purely to satisfy the DT schema and
scripts/checkpatch.pl checks for undocumented compatibles.  For
ltr,ltrf216a this also documents the consensus: compatible is allowed
only via ACPI PRP0001, but not bindings.

Link: https://lore.kernel.org/all/20240705095047.90558-1-marex@denx.de/
Link: https://lore.kernel.org/lkml/20220731173446.7400bfa8@jic23-huawei/T/#me55be502302d70424a85368c2645c89f860b7b40
Cc: Marek Vasut <marex@denx.de>
Cc: Jonathan Cameron <jic23@kernel.org>
Cc: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240712121146.90942-1-krzysztof.kozlowski@linaro.orgSigned-off-by: Rob Herring (Arm) <robh@kernel.org>

Documentation/devicetree/bindings/incomplete-devices.yaml

+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/incomplete-devices.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Rejected, Legacy or Incomplete Devices
+
+maintainers:
+  - Rob Herring <robh@kernel.org>
+
+description:
+  Some devices will not or should not get a proper Devicetree bindings, but
+  their compatibles are present in Linux drivers for various reasons.
+
+  Examples are devices using ACPI PRP0001 with non-updatable firmware/ACPI
+  tables or old PowerPC platforms without in-tree DTS.
+
+  Following list of devices is an incomplete schema with a goal to pass DT schema
+  checks on 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.
+
+properties:
+  compatible:
+    oneOf:
+      - description:
+          Rejected compatibles in Devicetree, but used in ACPI-based devices
+          with non-updatable firmware/ACPI tables (via ACPI PRP0001)
+        enum:
+          - broadcom,bcm5241
+          - ltr,ltrf216a
+
+      - description: Legacy compatibles used on Macintosh devices
+        enum:
+          - adm1030
+          - bmac+
+          - heathrow-media-bay
+          - keylargo-media-bay
+          - lm87cimt
+          - MAC,adm1030
+          - MAC,ds1775
+          - max6690
+          - ohare-media-bay
+          - ohare-swim3
+          - smu-sat
+          - swim3
+
+      - description: Legacy compatibles used on other PowerPC devices
+        enum:
+          - 1682m-rng
+          - IBM,lhca
+          - IBM,lhea
+          - IBM,lhea-ethernet
+          - mpc5200b-fec-phy
+          - mpc5200-serial
+          - mpc5200-sram
+          - ohci-be
+          - ohci-bigendian
+          - ohci-le
+
+      - description: Legacy compatibles used on SPARC devices
+        enum:
+          - bq4802
+          - ds1287
+          - isa-m5819p
+          - isa-m5823p
+          - m5819
+          - sab82532
+          - SUNW,bbc-beep
+          - SUNW,bbc-i2c
+          - SUNW,CS4231
+          - SUNW,ebus-pic16f747-env
+          - SUNW,kt-cwq
+          - SUNW,kt-mau
+          - SUNW,n2-cwq
+          - SUNW,n2-mau
+          - SUNW,niusl
+          - SUNW,smbus-beep
+          - SUNW,sun4v-console
+          - SUNW,sun4v-pci
+          - SUNW,vf-cwq
+          - SUNW,vf-mau
+
+      - description: Incomplete and/or legacy compatibles for unknown devices
+        enum:
+          - electra-cf
+          - i2cpcf,8584
+          - virtio,uml
+
+      - description: Linux kernel unit tests and sample code
+        enum:
+          - audio-graph-card2-custom-sample
+          - compat1
+          - compat2
+          - compat3
+          - linux,spi-loopback-test
+          - mailbox-test
+          - regulator-virtual-consumer
+
+      - description:
+          Devices on MIPS platform, without any DTS users.  These are
+          unlikely to get converted to DT schema.
+        enum:
+          - mti,ranchu
+
+      - description:
+          Devices on PowerPC platform, without any DTS users.  These are
+          unlikely to get converted to DT schema.
+        enum:
+          - fujitsu,coral
+          - fujitsu,lime
+          - fujitsu,MB86276
+          - fujitsu,MB86277
+          - fujitsu,MB86293
+          - fujitsu,MB86294
+          - fujitsu,mint
+          - ibm,axon-msic
+          - ibm,pmemory
+          - ibm,pmemory-v2
+          - ibm,power-rng
+          - ibm,ppc4xx-spi
+          - ibm,sdram-4xx-ddr2
+          - ibm,secureboot
+          - ibm,secureboot-v1
+          - ibm,secureboot-v2
+          - ibm,secvar-backend
+          - sgy,gpio-halt
+          - wrs,epld-localbus
+
+required:
+  - compatible
+  - broken-usage-of-incorrect-compatible
+
+additionalProperties: false