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SubjectRe: [PATCH V9 1/2] dt-bindings: mailbox: add binding doc for the ARM SMC/HVC mailbox
On Wed, 25 Sep 2019 02:09:08 +0000
Peng Fan <peng.fan@nxp.com> wrote:

Hi,

> From: Peng Fan <peng.fan@nxp.com>
>
> The ARM SMC/HVC mailbox binding describes a firmware interface to trigger
> actions in software layers running in the EL2 or EL3 exception levels.
> The term "ARM" here relates to the SMC instruction as part of the ARM
> instruction set, not as a standard endorsed by ARM Ltd.
>
> Signed-off-by: Peng Fan <peng.fan@nxp.com>
> Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
> ---
> .../devicetree/bindings/mailbox/arm-smc.yaml | 96 ++++++++++++++++++++++
> 1 file changed, 96 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/mailbox/arm-smc.yaml
>
> diff --git a/Documentation/devicetree/bindings/mailbox/arm-smc.yaml b/Documentation/devicetree/bindings/mailbox/arm-smc.yaml
> new file mode 100644
> index 000000000000..b061954d1678
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mailbox/arm-smc.yaml
> @@ -0,0 +1,96 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/mailbox/arm-smc.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: ARM SMC Mailbox Interface
> +
> +maintainers:
> + - Peng Fan <peng.fan@nxp.com>
> +
> +description: |
> + This mailbox uses the ARM smc (secure monitor call) or hvc (hypervisor
> + call) instruction to trigger a mailbox-connected activity in firmware,
> + executing on the very same core as the caller. The value of r0/w0/x0
> + the firmware returns after the smc call is delivered as a received
> + message to the mailbox framework, so synchronous communication can be
> + established. The exact meaning of the action the mailbox triggers as
> + well as the return value is defined by their users and is not subject
> + to this binding.
> +
> + One example use case of this mailbox is the SCMI 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.
> + Upon receiving an SMC using the described SMC function identifier, the
> + firmware is expected to trigger some mailbox connected functionality.
> + The communication follows the ARM SMC calling convention.
> + Firmware expects an SMC function identifier in r0 or w0. The supported
> + identifier are passed from consumers, or listed in the the arm,func-id
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This is now obsolete.
The rest looks good to me, thanks for the changes!

Reviewed-by: Andre Przywara <andre.przywara@arm.com>

Cheers,
Andre.

> + property as described below. The firmware can return one value in
> + the first SMC result register, it is expected to be an error value,
> + which shall be propagated to the mailbox client.
> +
> + 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.
> +
> +properties:
> + compatible:
> + oneOf:
> + - description:
> + For implementations using ARM SMC instruction.
> + const: arm,smc-mbox
> +
> + - description:
> + For implementations using ARM HVC instruction.
> + const: arm,hvc-mbox
> +
> + "#mbox-cells":
> + const: 0
> +
> + arm,func-id:
> + description: |
> + An single 32-bit value specifying the function ID used by the mailbox.
> + The function ID follows the ARM SMC calling convention standard.
> + $ref: /schemas/types.yaml#/definitions/uint32
> +
> +required:
> + - compatible
> + - "#mbox-cells"
> + - arm,func-id
> +
> +examples:
> + - |
> + sram@93f000 {
> + compatible = "mmio-sram";
> + reg = <0x0 0x93f000 0x0 0x1000>;
> + #address-cells = <1>;
> + #size-cells = <1>;
> + ranges = <0x0 0x93f000 0x1000>;
> +
> + cpu_scp_lpri: scp-shmem@0 {
> + compatible = "arm,scmi-shmem";
> + reg = <0x0 0x200>;
> + };
> + };
> +
> + smc_tx_mbox: tx_mbox {
> + #mbox-cells = <0>;
> + compatible = "arm,smc-mbox";
> + arm,func-id = <0xc20000fe>;
> + };
> +
> + firmware {
> + scmi {
> + compatible = "arm,scmi";
> + mboxes = <&smc_tx_mbox>;
> + mbox-names = "tx";
> + shmem = <&cpu_scp_lpri>;
> + };
> + };
> +
> +...

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