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Date: Mon, 3 Apr 2023 14:58:08 -0500
From: Rob Herring <robh@...nel.org>
To: Cristian Marussi <cristian.marussi@....com>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
devicetree@...r.kernel.org, sudeep.holla@....com,
vincent.guittot@...aro.org, souvik.chakravarty@....com,
nicola.mazzucato@....com, krzysztof.kozlowski+dt@...aro.org
Subject: Re: [PATCH v2 1/2] dt-bindings: firmware: arm,scmi: Support
mailboxes unidirectional channels
On Mon, Mar 27, 2023 at 04:45:27PM +0100, Cristian Marussi wrote:
> SCMI defines two kinds of communication channels between the agent and the
> platform: one bidirectional 'a2p' channel used by the agent to send SCMI
> commands and synchronously receive the related replies, and an optional
> 'p2a' unidirectional channel used to asynchronously receive delayed
> responses and notifications emitted from the platform.
>
> When configuring an SCMI transport based on mailboxes, the current binding
> supports only mailboxes providing bidirectional channels: in such a case
> one mailbox channel can be easily assigned to each SCMI channel as above
> described.
>
> In case, instead, to have to deal with mailboxes providing only distinct
> unidirectional channels, it becomes necessary to extend the binding in
> order to be able to bind 2 distinct unidirectional mailbox channels to the
> same SCMI 'a2p' channel.
>
> Bidirectional and unidirectional channels support for the SCMI mailbox
> transport can coexist by carefully considering the effective combination
> of defined 'mboxes' and 'shmem' descriptors.
>
> Signed-off-by: Cristian Marussi <cristian.marussi@....com>
> ---
> v1 --> v2
> - added mbox-names unidirectional definitions and example
> ---
> .../bindings/firmware/arm,scmi.yaml | 76 ++++++++++++++++---
> 1 file changed, 66 insertions(+), 10 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/firmware/arm,scmi.yaml b/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> index 2f7c51c75e85..0204b102b47f 100644
> --- a/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> +++ b/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> @@ -56,17 +56,41 @@ properties:
> description:
> Specifies the mailboxes used to communicate with SCMI compliant
> firmware.
> - items:
> - - const: tx
> - - const: rx
> + oneOf:
> + - items:
> + - const: tx
> + - items:
> + - const: tx
> + - const: rx
These 2 'items' can be collapsed to 1 with 'minItems: 1' added.
> + - items:
> + - const: tx
> + - const: tx_reply
> + - items:
> + - const: tx
> + - const: tx_reply
> + - const: rx
Same on these 2 with 'minItems: 2' added.
>
> mboxes:
> description:
> List of phandle and mailbox channel specifiers. It should contain
> - exactly one or two mailboxes, one for transmitting messages("tx")
> - and another optional for receiving the notifications("rx") if supported.
> + exactly one, two or three mailboxes; the first one or two for transmitting
> + messages ("tx") and another optional ("rx") for receiving notifications
> + and delayed responses, if supported by the platform.
> + The number of mailboxes needed for transmitting messages depends on the
> + type of channels exposed by the specific underlying mailbox controller;
> + one single channel descriptor is enough if such channel is bidirectional,
> + while two channel descriptors are needed to represent the SCMI ("tx")
> + channel if the underlying mailbox channels are of unidirectional type.
> + The effective combination in numbers of mboxes and shmem descriptors let
> + the SCMI subsystem determine unambiguosly which type of SCMI channels are
> + made available by the underlying mailbox controller and how to use them.
> + 1 mbox / 1 shmem => SCMI TX over 1 mailbox bidirectional channel
> + 2 mbox / 2 shmem => SCMI TX and RX over 2 mailbox bidirectional channels
> + 2 mbox / 1 shmem => SCMI TX over 2 mailbox unidirectional channels
> + 3 mbox / 2 shmem => SCMI TX and RX over 3 mailbox unidirectional channels
> + Any other combination of mboxes and shmem is invalid.
> minItems: 1
> - maxItems: 2
> + maxItems: 3
>
> shmem:
> description:
> @@ -228,13 +252,23 @@ $defs:
> maxItems: 1
>
> mbox-names:
> - items:
> - - const: tx
> - - const: rx
> + oneOf:
> + - items:
> + - const: tx
> + - items:
> + - const: tx
> + - const: rx
> + - items:
> + - const: tx
> + - const: tx_reply
> + - items:
> + - const: tx
> + - const: tx_reply
> + - const: rx
>
> mboxes:
> minItems: 1
> - maxItems: 2
> + maxItems: 3
>
> shmem:
> minItems: 1
> @@ -393,6 +427,28 @@ examples:
> };
> };
>
> + - |
> + firmware {
> + scmi {
> + compatible = "arm,scmi";
> + mboxes = <&mhu_U_tx 0 0>, <&mhu_U_rx 0 0>;
> + mbox-names = "tx", "tx_reply";
> + shmem = <&cpu_scp_lpri0>;
> +
> + #address-cells = <1>;
> + #size-cells = <0>;
> +
> + scmi_dvfs_2: protocol@13 {
> + reg = <0x13>;
> + #clock-cells = <1>;
> +
> + mboxes = <&mhu_U_tx 1 0>, <&mhu_U_rx 1 0>, <&mhu_U_rx 1 1>;
> + mbox-names = "tx", "tx_reply", "rx";
> + shmem = <&cpu_scp_hpri0>, <&cpu_scp_hpri1>;
> + };
> + };
> + };
> +
> - |
> firmware {
> scmi {
> --
> 2.34.1
>
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