dt-bindings: firmware: arm,scmi: Document arm,no-completion-irq property

Document new property arm,no-completion-irq . This optional property
is intended for hardware that does not generate completion interrupts
and can be used to unconditionally enable forced polling mode of
operation.

With this property set, such implementations which do not generate
interrupts can be interacted with, until they are fixed to generate
interrupts properly.

Note that, because the original base protocol exchange also requires
some sort of completion mechanism, it is not possible to query SCMI
itself for this property and it must be described in DT. While this
does look a bit like policy, the SCMI provider is part of the
hardware, hence DT.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Message-Id: <20260117010241.186685-1-marek.vasut+renesas@mailbox.org>
Signed-off-by: Sudeep Holla <sudeep.holla@kernel.org>

Documentation/devicetree/bindings/firmware/arm,scmi.yaml

@@ -146,6 +146,13 @@ properties:
       this platform. If set, the value should be non-zero.
     minimum: 1
 
+  arm,no-completion-irq:
+    type: boolean
+    description:
+      This optional property is intended for hardware that does not generate
+      completion interrupts and can be used to unconditionally enable forced
+      polling mode of operation.
+
   arm,smc-id:
     $ref: /schemas/types.yaml#/definitions/uint32
     description:
@@ -379,6 +386,9 @@ then:
     - shmem
 
 else:
+  properties:
+    arm,no-completion-irq: false
+
   if:
     properties:
       compatible: