[PATCH 2/8] dt-bindings: mailbox: add binding doc for the ARM SMC mailbox

[Rob Herring]

On Fri, Jun 30, 2017 at 10:56:02AM +0100, Andre Przywara wrote:
> Add binding documentation for the generic ARM SMC mailbox.
> This is not describing hardware, but a firmware interface.
> 
> Signed-off-by: Andre Przywara <andre.przywara at arm.com>
> ---
>  .../devicetree/bindings/mailbox/arm-smc.txt        | 61 ++++++++++++++++++++++
>  1 file changed, 61 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/mailbox/arm-smc.txt
> 
> diff --git a/Documentation/devicetree/bindings/mailbox/arm-smc.txt b/Documentation/devicetree/bindings/mailbox/arm-smc.txt
> new file mode 100644
> index 0000000..90c5926
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mailbox/arm-smc.txt
> @@ -0,0 +1,61 @@
> +ARM SMC Mailbox Driver

s/Driver/Interface/

> +======================
> +
> +This mailbox uses the ARM smc (secure monitor call) instruction to
> +trigger a mailbox-connected activity in firmware, executing on the very same
> +core as the caller. By nature this operation is synchronous and this
> +mailbox provides no way for asynchronous messages to be delivered the other
> +way round, from firmware to the OS. However the value of r0/w0/x0 the firmware
> +returns after the smc call is delivered as a received message to the
> +mailbox framework, so a synchronous communication can be established.
> +
> +One use case of this mailbox is the SCP interface, which uses shared memory
> +to transfer commands and parameters, and a mailbox to trigger a function
> +call. This allows SoCs without a separate management processor (or
> +when such a processor is not available or used) to use this standardized
> +interface anyway.
> +
> +This binding describes no hardware, but establishes a firmware interface.
> +The communication follows the ARM SMC calling convention[1].
> +Any core which supports the SMC or HVC instruction can be used, as long as
> +a firmware component running in EL3 or EL2 is handling these calls.
> +
> +Mailbox Device Node:
> +====================

Please state this should be a child of /firmware node.

> +
> +Required properties:
> +--------------------
> +- compatible:		Shall be "arm,smc-mbox"
> +- #mbox-cells		Shall be 1 - the index of the channel needed.
> +- arm,smc-func-ids	An array of 32-bit values specifying the function
> +			IDs used by each mailbox channel. Those function IDs
> +			follow the ARM SMC calling convention standard [1].
> +			There is one identifier per channel and the number
> +			of supported channels is determined by the length
> +			of this array.
> +
> +Optional properties:
> +--------------------
> +- method:		A string, either:
> +			"hvc": if the driver shall use an HVC call, or
> +			"smc": if the driver shall use an SMC call
> +			If omitted, defaults to an SMC call.
> +
> +Example:
> +--------
> +
> +	mailbox: smc_mbox {

swap these. mailbox for the node name.

> +		#mbox-cells = <1>;
> +		compatible = "arm,smc-mbox";
> +		identifiers = <0x82000001>, <0x82000002>;
> +	};
> +
> +	scpi {
> +		compatible = "arm,scpi";
> +		mboxes = <&mailbox 0>;
> +		shmem = <&cpu_scp_shmem>;
> +	};
> +
> +
> +[1]
> +http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.den0028a/index.html
> -- 
> 2.9.0
>