linux-kernel - Re: [PATCH 3/3] dt-bindings: mfd: add "syscon-smc" YAML description

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Date:   Thu, 29 Jul 2021 15:19:19 -0600
From:   Rob Herring <robh@...nel.org>
To:     Clément Léger <clement.leger@...tlin.com>
Cc:     Lee Jones <lee.jones@...aro.org>, Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Peng Fan <peng.fan@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
Subject: Re: [PATCH 3/3] dt-bindings: mfd: add "syscon-smc" YAML description

On Fri, Jul 23, 2021 at 03:52:39PM +0200, Clément Léger wrote:
> This patch adds documentation for the "syscon-smc" compatible which describes
> a syscon using a SMC regmap instead of a MMIO one. This allows accessing system
> controllers that are set as secure by using SMC handled by the secure monitor.
> 
> Signed-off-by: Clément Léger <clement.leger@...tlin.com>
> ---
>  .../devicetree/bindings/mfd/syscon-smc.yaml   | 57 +++++++++++++++++++
>  1 file changed, 57 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/mfd/syscon-smc.yaml
> 
> diff --git a/Documentation/devicetree/bindings/mfd/syscon-smc.yaml b/Documentation/devicetree/bindings/mfd/syscon-smc.yaml
> new file mode 100644
> index 000000000000..6ce1392c5e7f
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mfd/syscon-smc.yaml
> @@ -0,0 +1,57 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/mfd/syscon-smc.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: System Controller Registers R/W via SMC Device Tree Bindings
> +
> +description: |
> +  System controller SMC node represents a register region containing a set
> +  of miscellaneous registers accessed through a secure monitor.
> +  The typical use-case is the same as the syscon one but when running with a
> +  secure monitor.
> +
> +maintainers:
> +  - Lee Jones <lee.jones@...aro.org>
> +
> +properties:
> +  compatible:
> +    anyOf:
> +      - items:
> +          - enum:
> +              - atmel,sama5d2-sfr
> +
> +          - const: syscon-smc

I regret having 'syscon' as a compatible, so nak on a 2nd flavor of it. 
It's only purpose is a hint to Linux to automagically create a regmap for 
you.

All you need is the specific compatible, atmel,sama5d2-sfr, and you can 
imply the rest of this from it. That's assuming the conclusion is a 
register read/write interface on SMC is a good idea, but I don't think 
it is.

Rob