Re: [PATCH v4 1/2] dt-bindings: timer: thead,c900-aclint-mtimer: separate mtime and mtimecmp regs

[Anup Patel]

On Sat, Nov 18, 2023 at 12:39 PM Inochi Amaoto <inochiama@xxxxxxxxxxx> wrote:
>
> The timer registers of aclint don't follow the clint layout and can
> be mapped on any different offset. As sg2042 uses separated timer
> and mswi for its clint, it should follow the aclint spec and have
> separated registers.
>
> The previous patch introduced a new type of T-HEAD aclint timer which
> has clint timer layout. Although it has the clint timer layout, it
> should follow the aclint spec and uses the separated mtime and mtimecmp
> regs. So a ABI change is needed to make the timer fit the aclint spec.
>
> To make T-HEAD aclint timer more closer to the aclint spec, use
> regs-names to represent the mtimecmp register, which can avoid hack
> for unsupport mtime register of T-HEAD aclint timer.
>
> Signed-off-by: Inochi Amaoto <inochiama@xxxxxxxxxxx>
> Fixes: 4734449f7311 ("dt-bindings: timer: Add Sophgo sg2042 CLINT timer")
> Link: https://lists.infradead.org/pipermail/opensbi/2023-October/005693.html
> Link: https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc

The ratified Priv v1.12 specification defines platform specific M-mode timer
registers without defining any layout of mtime and mtimecmp registers.
(Refer, "3.2.1 Machine Timer Registers (mtime and mtimecmp)")

The "thead,c900-aclint-mtimer" can be thought of as is one possible
implementation of "riscv,mtimer" defined by the Priv v1.12 specificaiton.

If it is not too late then I suggest making this binding into generic
"riscv,mtimer" binding.

Regards,
Anup

> ---
>  .../timer/thead,c900-aclint-mtimer.yaml       | 42 ++++++++++++++++++-
>  1 file changed, 41 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/devicetree/bindings/timer/thead,c900-aclint-mtimer.yaml b/Documentation/devicetree/bindings/timer/thead,c900-aclint-mtimer.yaml
> index fbd235650e52..053488fb1286 100644
> --- a/Documentation/devicetree/bindings/timer/thead,c900-aclint-mtimer.yaml
> +++ b/Documentation/devicetree/bindings/timer/thead,c900-aclint-mtimer.yaml
> @@ -17,7 +17,20 @@ properties:
>        - const: thead,c900-aclint-mtimer
>
>    reg:
> -    maxItems: 1
> +    oneOf:
> +      - items:
> +          - description: MTIME Registers
> +          - description: MTIMECMP Registers
> +      - items:
> +          - description: MTIMECMP Registers
> +
> +  reg-names:
> +    oneOf:
> +      - items:
> +          - const: mtime
> +          - const: mtimecmp
> +      - items:
> +          - const: mtimecmp
>
>    interrupts-extended:
>      minItems: 1
> @@ -28,8 +41,34 @@ additionalProperties: false
>  required:
>    - compatible
>    - reg
> +  - reg-names
>    - interrupts-extended
>
> +allOf:
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            const: thead,c900-aclint-mtimer
> +    then:
> +      properties:
> +        reg:
> +          items:
> +            - description: MTIMECMP Registers
> +        reg-names:
> +          items:
> +            - const: mtimecmp
> +    else:
> +      properties:
> +        reg:
> +          items:
> +            - description: MTIME Registers
> +            - description: MTIMECMP Registers
> +        reg-names:
> +          items:
> +            - const: mtime
> +            - const: mtimecmp
> +
>  examples:
>    - |
>      timer@ac000000 {
> @@ -39,5 +78,6 @@ examples:
>                              <&cpu3intc 7>,
>                              <&cpu4intc 7>;
>        reg = <0xac000000 0x00010000>;
> +      reg-names = "mtimecmp";
>      };
>  ...
> --
> 2.42.1
>
>