Re: [RFC PATCH 06/11] dt-bindings: soc: microchip: document the two simple-mfd syscons on PolarFire SoC

[Conor Dooley <conor@kernel.org>]

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On Thu, Aug 15, 2024 at 03:01:09PM +0100, Conor Dooley wrote:
> From: Conor Dooley <conor.dooley@microchip.com>
> 
> There are two syscons on PolarFire SoC that provide various functionality of
> use to the OS.
> 
> The first of these is the "control-scb" region, that contains the "tvs"
> temperature and voltage sensors and the control/status registers for the
> system controller's mailbox. The mailbox has a dedicated node, so
> there's no need for a child node describing it, looking the syscon up by
> compatible is sufficient.
> 
> The second, "mss-top-sysreg", contains clocks, pinctrl, resets, and
> interrupt controller and more. For this RFC, only the reset controller
> child is described as that's all that is described by the existing
> bindings. The clock controller already has a dedicated node, and will
> retain it as there are other clock regions, so like the mailbox,
> a compatible-based lookup of the syscon is sufficient to keep the clock
> driver working as before so no child is needed.
> 
> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> ---
> (I'll split this in two later, it's just easier when I have the same
> questions about both...)
> 
> Are these things entitled to have child nodes for the reset and sensor
> nodes, or should the properties be in the parent and the OS probe the
> drivers for the functions? That's something that, despite supposedly
> being a maintainer, I do not understand the rules (of thumb?) for.

After posting a link to this on the devicetree irc channel, I had some
discussion with Mark Brown about whether or not the functions described
by the child nodes were ever likely to be independently reused. Given that
they're pretty closely tied to the integration of this particular SoC-FPGA
I think it is unlikely to happen. Reading between the lines, I'm going
to chalk that up as one vote against child nodes being suitable here.

Cheers,
Conor.

> 
> Secondly, is it okay to make the "pragmatic" decision to not have a
> child clock node and keep routing the clocks via the existing & retained
> clock node (and therefore not update the various clocks nodes in the
> consumers)? Doing so would require a lot more hocus pocus with the clock
> driver than this series does, as the same driver would no longer be
> suitable for the before/after bindings.
>
> ---
>  .../microchip/microchip,mpfs-control-scb.yaml | 54 +++++++++++++++++++
>  .../microchip,mpfs-mss-top-sysreg.yaml        | 53 ++++++++++++++++++
>  2 files changed, 107 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/soc/microchip/microchip,mpfs-control-scb.yaml
>  create mode 100644 Documentation/devicetree/bindings/soc/microchip/microchip,mpfs-mss-top-sysreg.yaml
> 
> diff --git a/Documentation/devicetree/bindings/soc/microchip/microchip,mpfs-control-scb.yaml b/Documentation/devicetree/bindings/soc/microchip/microchip,mpfs-control-scb.yaml
> new file mode 100644
> index 000000000000..3673bf139ce8
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/soc/microchip/microchip,mpfs-control-scb.yaml
> @@ -0,0 +1,54 @@
> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/soc/microchip/microchip,mpfs-control-scb.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Microchip PolarFire SoC System Controller Bus (SCB) Control Register region
> +
> +maintainers:
> +  - Conor Dooley <conor.dooley@microchip.com>
> +
> +description:
> +  An assortment of system controller related registers, including voltage and
> +  temperature sensors and the status/control registers for the system
> +  controller's mailbox.
> +
> +properties:
> +  compatible:
> +    items:
> +      - const: microchip,mpfs-control-scb
> +      - const: syscon
> +      - const: simple-mfd
> +
> +  reg:
> +    maxItems: 1
> +
> +  sensor:
> +    type: object
> +
> +    properties:
> +      compatible:
> +        const: microchip,mpfs-tvs
> +
> +    additionalProperties: false
> +
> +required:
> +  - compatible
> +  - reg
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    soc {
> +      syscon@37020000 {
> +        compatible = "microchip,mpfs-control-scb", "syscon", "simple-mfd";
> +        reg = <0x37020000 0x100>;
> +
> +        sensor {
> +          compatible = "microchip,mpfs-tvs";
> +        };
> +      };
> +    };
> +
> diff --git a/Documentation/devicetree/bindings/soc/microchip/microchip,mpfs-mss-top-sysreg.yaml b/Documentation/devicetree/bindings/soc/microchip/microchip,mpfs-mss-top-sysreg.yaml
> new file mode 100644
> index 000000000000..d70c9c3348ac
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/soc/microchip/microchip,mpfs-mss-top-sysreg.yaml
> @@ -0,0 +1,53 @@
> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/soc/microchip/microchip,mpfs-mss-top-sysreg.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Microchip PolarFire SoC Microprocessor Subsystem (MSS) sysreg Register region
> +
> +maintainers:
> +  - Conor Dooley <conor.dooley@microchip.com>
> +
> +description:
> +  An wide assortment of registers that control elements of the MSS on PolarFire
> +  SoC, including pinmuxing, resets and clocks among others.
> +
> +properties:
> +  compatible:
> +    items:
> +      - const: microchip,mpfs-mss-top-sysreg
> +      - const: syscon
> +      - const: simple-mfd
> +
> +  reg:
> +    maxItems: 1
> +
> +  reset-controller:
> +    type: object
> +
> +    properties:
> +      compatible:
> +        const: microchip,mpfs-reset
> +
> +      '#reset-cells':
> +        description:
> +          The AHB/AXI peripherals on the PolarFire SoC have reset support, so
> +          from CLK_ENVM to CLK_CFM. The reset consumer should specify the
> +          desired peripheral via the clock ID in its "resets" phandle cell.
> +          See include/dt-bindings/clock/microchip,mpfs-clock.h for the full list
> +          of PolarFire clock/reset IDs.
> +        const: 1
> +
> +    additionalProperties: false
> +required:
> +  - compatible
> +  - reg
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    soc {
> +    };
> +
> -- 
> 2.43.0
> 

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