linux-kernel - Re: [PATCH V10 1/2] dt-bindings: mailbox: add binding doc for the ARM SMC/HVC mailbox

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Message-ID: <20190930142640.GA24945@bogus>
Date:   Mon, 30 Sep 2019 15:26:40 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Peng Fan <peng.fan@....com>
Cc:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "jassisinghbrar@...il.com" <jassisinghbrar@...il.com>,
        "andre.przywara@....com" <andre.przywara@....com>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        dl-linux-imx <linux-imx@....com>,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH V10 1/2] dt-bindings: mailbox: add binding doc for the
 ARM SMC/HVC mailbox

On Mon, Sep 30, 2019 at 06:20:09AM +0000, Peng Fan wrote:
> From: Peng Fan <peng.fan@....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.
> 

FWIW:

Reviewed-by: Sudeep Holla <sudeep.holla@....com>

> Reviewed-by: Rob Herring <robh@...nel.org>
> Reviewed-by: Andre Przywara <andre.przywara@....com>
> Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
> Signed-off-by: Peng Fan <peng.fan@....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..c165946a64e4
> --- /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@....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 is listed in the the arm,func-id 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@...000 {
> +      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 {

[nit]              ^^^^^^^^^ s/tx_mbox/mailbox/ ?

mailbox sounds more generic name to use, you can always use what ever
name in the label. This is not a must change, just thought of mentioning
as the pattern followed is to use generic names.

--
Regards,
Sudeep