dt-bindings: mailbox: Add mediatek,gce-props.yaml

Add mediatek,gce-props.yaml for common GCE properties that is used for
both mailbox providers and consumers. We place the common property
"mediatek,gce-events" in this binding currently.

The property "mediatek,gce-events" is used for GCE event ID corresponding
to a hardware event signal sent by the hardware or a software driver.
If the mailbox providers or consumers want to manipulate the value of
the event ID, they need to know the specific event ID.

Signed-off-by: Jason-JH.Lin <[e-mail]>
Reviewed-by: Conor Dooley <[e-mail]>
Reviewed-by: AngeloGioacchino Del Regno <[e-mail]>
Signed-off-by: Jassi Brar <[e-mail]>

Documentation/devicetree/bindings/mailbox/mediatek,gce-props.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mailbox/mediatek,gce-props.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MediaTek Global Command Engine Common Properties
+
+maintainers:
+  - Houlong Wei <[e-mail]>
+
+description:
+  The Global Command Engine (GCE) is an instruction based, multi-threaded,
+  single-core command dispatcher for MediaTek hardware. The Command Queue
+  (CMDQ) mailbox driver is a driver for GCE, implemented using the Linux
+  mailbox framework. It is used to receive messages from mailbox consumers
+  and configure GCE to execute the specified instruction set in the message.
+  We use mediatek,gce-mailbox.yaml to define the properties for CMDQ mailbox
+  driver. A device driver that uses the CMDQ driver to configure its hardware
+  registers is a mailbox consumer. The mailbox consumer can request a mailbox
+  channel corresponding to a GCE hardware thread to send a message, specifying
+  that the GCE thread to configure its hardware. The mailbox provider can also
+  reserve a mailbox channel to configure GCE hardware register by the specific
+  GCE thread. This binding defines the common GCE properties for both mailbox
+  provider and consumers.
+
+properties:
+  mediatek,gce-events:
+    description:
+      GCE has an event table in SRAM, consisting of 1024 event IDs (0~1023).
+      Each event ID has a boolean event value with the default value 0.
+      The property mediatek,gce-events is used to obtain the event IDs.
+      Some gce-events are hardware-bound and cannot be changed by software.
+      For instance, in MT8195, when VDO0_MUTEX is stream done, VDO_MUTEX will
+      send an event signal to GCE, setting the value of event ID 597 to 1.
+      Similarly, in MT8188, the value of event ID 574 will be set to 1 when
+      VOD0_MUTEX is stream done.
+      On the other hand, some gce-events are not hardware-bound and can be
+      changed by software. For example, in MT8188, we can set the value of
+      event ID 855, which is not bound to any hardware, to 1 when the driver
+      in the secure world completes a task. However, in MT8195, event ID 855
+      is already bound to VDEC_LAT1, so we need to select another event ID to
+      achieve the same purpose. This event ID can be any ID that is not bound
+      to any hardware and is not yet used in any software driver.
+      To determine if the event ID is bound to the hardware or used by a
+      software driver, refer to the GCE header
+      include/dt-bindings/gce/<chip>-gce.h of each chip.
+    $ref: /schemas/types.yaml#/definitions/uint32-array
+    minItems: 1
+    maxItems: 32
+
+additionalProperties: true