linux-kernel - Re: [PATCH v6 1/7] dt-bindings: reset: microchip,rst: Allow to replace cpu-syscon by an additional reg item

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Message-ID: <emcl3vfclrmy273kknsakpqpzolvo5vohrjnw64ml3op4dwzvu@lwqfgc7jxxzq>
Date: Tue, 1 Oct 2024 08:43:23 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Herve Codina <herve.codina@...tlin.com>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>, 
	Andy Shevchenko <andy.shevchenko@...il.com>, Simon Horman <horms@...nel.org>, Lee Jones <lee@...nel.org>, 
	Arnd Bergmann <arnd@...db.de>, Derek Kiernan <derek.kiernan@....com>, 
	Dragan Cvetic <dragan.cvetic@....com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Philipp Zabel <p.zabel@...gutronix.de>, 
	Lars Povlsen <lars.povlsen@...rochip.com>, Steen Hegelund <Steen.Hegelund@...rochip.com>, 
	Daniel Machon <daniel.machon@...rochip.com>, UNGLinuxDriver@...rochip.com, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Saravana Kannan <saravanak@...gle.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Horatiu Vultur <horatiu.vultur@...rochip.com>, 
	Andrew Lunn <andrew@...n.ch>, devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	netdev@...r.kernel.org, linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	Allan Nielsen <allan.nielsen@...rochip.com>, Luca Ceresoli <luca.ceresoli@...tlin.com>, 
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v6 1/7] dt-bindings: reset: microchip,rst: Allow to
 replace cpu-syscon by an additional reg item

On Mon, Sep 30, 2024 at 02:15:41PM +0200, Herve Codina wrote:
> In the LAN966x PCI device use case, syscon cannot be used as syscon
> devices do not support removal [1]. A syscon device is a core "system"
> device and not a device available in some addon boards and so, it is not
> supposed to be removed.

That's not accurate. syscon is our own, Linux term which means also
anything exposing set of registers.

If you need to unload syscons, implement it. syscon is the same resource
as all others so should be handled same way.

> 
> In order to remove the syscon device usage, allow the reset controller
> to have a direct access to the address range it needs to use.

So you map same address twice? That's not good, because you have no
locking over concurrent register accesses.

> 
> Link: https://lore.kernel.org/all/20240923100741.11277439@bootlin.com/ [1]
> Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> ---
>  .../bindings/reset/microchip,rst.yaml         | 35 ++++++++++++++++++-
>  1 file changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/reset/microchip,rst.yaml b/Documentation/devicetree/bindings/reset/microchip,rst.yaml
> index f2da0693b05a..5164239a372c 100644
> --- a/Documentation/devicetree/bindings/reset/microchip,rst.yaml
> +++ b/Documentation/devicetree/bindings/reset/microchip,rst.yaml
> @@ -25,12 +25,16 @@ properties:
>        - microchip,lan966x-switch-reset
>  
>    reg:
> +    minItems: 1
>      items:
>        - description: global control block registers
> +      - description: cpu system block registers
>  
>    reg-names:
> +    minItems: 1
>      items:
>        - const: gcb
> +      - const: cpu
>  
>    "#reset-cells":
>      const: 1
> @@ -39,12 +43,29 @@ properties:
>      $ref: /schemas/types.yaml#/definitions/phandle
>      description: syscon used to access CPU reset
>  
> +allOf:
> +  # Allow to use the second reg item instead of cpu-syscon
> +  - if:
> +      required:
> +        - cpu-syscon
> +    then:
> +      properties:
> +        reg:
> +          maxItems: 1
> +        reg-names:
> +          maxItems: 1
> +    else:
> +      properties:
> +        reg:
> +          minItems: 2
> +        reg-names:
> +          minItems: 2
> +
>  required:
>    - compatible
>    - reg
>    - reg-names
>    - "#reset-cells"
> -  - cpu-syscon
>  
>  additionalProperties: false
>  
> @@ -57,3 +78,15 @@ examples:
>          #reset-cells = <1>;
>          cpu-syscon = <&cpu_ctrl>;
>      };
> +
> +    /*
> +     * The following construction can be used if the cpu-syscon device is not
> +     * present. This is the case when the LAN966x is used as a PCI device.
> +     */
> +    reset-controller@...10008 {
> +        compatible = "microchip,lan966x-switch-reset";
> +        reg = <0xe200400c 0x4>,
> +              <0xe00c0000 0xa8>;

If you have here CPU address, then syscon device is present...

Best regards,
Krzysztof