linux-kernel - Re: [PATCH v4 2/3] dt-bindings: mailbox: Add thead,th1520-mailbox bindings

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Message-ID: <f1c1af8c-18e0-433d-a61c-90080919378f@sifive.com>
Date: Tue, 15 Oct 2024 18:14:28 -0500
From: Samuel Holland <samuel.holland@...ive.com>
To: Michal Wilczynski <m.wilczynski@...sung.com>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org,
 Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, drew@...7.com,
 guoren@...nel.org, wefu@...hat.com, jassisinghbrar@...il.com,
 robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
 paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu,
 m.szyprowski@...sung.com
Subject: Re: [PATCH v4 2/3] dt-bindings: mailbox: Add thead,th1520-mailbox
 bindings

Hi Michal,

On 2024-10-14 7:33 AM, Michal Wilczynski wrote:
> Add bindings for the mailbox controller. This work is based on the vendor
> kernel. [1]
> 
> Link: https://github.com/revyos/thead-kernel.git [1]
> 
> Signed-off-by: Michal Wilczynski <m.wilczynski@...sung.com>
> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> ---
>  .../bindings/mailbox/thead,th1520-mbox.yaml   | 80 +++++++++++++++++++
>  MAINTAINERS                                   |  1 +
>  2 files changed, 81 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/mailbox/thead,th1520-mbox.yaml
> 
> diff --git a/Documentation/devicetree/bindings/mailbox/thead,th1520-mbox.yaml b/Documentation/devicetree/bindings/mailbox/thead,th1520-mbox.yaml
> new file mode 100644
> index 000000000000..12507c426691
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mailbox/thead,th1520-mbox.yaml
> @@ -0,0 +1,80 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/mailbox/thead,th1520-mbox.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: T-head TH1520 Mailbox Controller
> +
> +description:
> +  The T-head mailbox controller enables communication and coordination between
> +  cores within the SoC by passing messages (e.g., data, status, and control)
> +  through mailbox channels. It also allows one core to signal another processor
> +  using interrupts via the Interrupt Controller Unit (ICU).
> +
> +maintainers:
> +  - Michal Wilczynski <m.wilczynski@...sung.com>
> +
> +properties:
> +  compatible:
> +    const: thead,th1520-mbox
> +
> +  reg:
> +    items:
> +      - description: Mailbox local base address
> +      - description: Remote ICU 0 base address
> +      - description: Remote ICU 1 base address
> +      - description: Remote ICU 2 base address

>From the SoC documentation, it looks like these are four different instances of
the same IP block, each containing 4 unidirectional mailbox channels and an
interrupt output. So these should be four separate nodes, no? The C910 would
receive on channels 1-3 of instance 0, and send on channel 0 of instances 1-3.

> +
> +  reg-names:
> +    items:
> +      - const: local
> +      - const: remote-icu0
> +      - const: remote-icu1
> +      - const: remote-icu2
> +
> +  interrupts:
> +    maxItems: 1
> +
> +  '#mbox-cells':
> +    const: 2
> +    description: |
> +      Specifies the number of cells needed to encode the mailbox specifier.
> +      The mailbox specifier consists of two cells:
> +        - Destination CPU ID.
> +        - Type, which can be one of the following:
> +            - 0:
> +                - TX & RX channels share the same channel.
> +                - Equipped with 7 info registers to facilitate data sharing.
> +                - Supports IRQ for signaling.
> +            - 1:
> +                - TX & RX operate as doorbell channels.
> +                - Does not have dedicated info registers.
> +                - Lacks ACK support.

It appears that these types are not describing hardware, but the protocol used
by the Linux driver to glue two unidirectional hardware channels together to
make a virtual bidirectional channel. This is really the responsibility of the
mailbox client to know what protocol it needs, not the devicetree.

Regards,
Samuel

> +
> +required:
> +  - compatible
> +  - reg
> +  - reg-names
> +  - interrupts
> +  - '#mbox-cells'
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +
> +    soc {
> +      #address-cells = <2>;
> +      #size-cells = <2>;
> +      mailbox@...fc38000 {
> +        compatible = "thead,th1520-mbox";
> +        reg = <0xff 0xffc38000 0x0 0x4000>,
> +              <0xff 0xffc44000 0x0 0x1000>,
> +              <0xff 0xffc4c000 0x0 0x1000>,
> +              <0xff 0xffc54000 0x0 0x1000>;
> +        reg-names = "local", "remote-icu0", "remote-icu1", "remote-icu2";
> +        interrupts = <28>;
> +        #mbox-cells = <2>;
> +      };
> +    };
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 0655c6ba5435..7401c7cb6533 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -19951,6 +19951,7 @@ L:	linux-riscv@...ts.infradead.org
>  S:	Maintained
>  T:	git https://github.com/pdp7/linux.git
>  F:	Documentation/devicetree/bindings/clock/thead,th1520-clk-ap.yaml
> +F:	Documentation/devicetree/bindings/mailbox/thead,th1520-mbox.yaml
>  F:	arch/riscv/boot/dts/thead/
>  F:	drivers/clk/thead/clk-th1520-ap.c
>  F:	drivers/mailbox/mailbox-th1520.c