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@xxxxxxx>
> ---
> .../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
>
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