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Date:   Fri, 7 Jul 2023 10:27:48 +0200
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Subject: Re: [PATCH v1 1/3] dt-bindings: usb: Add HPE GXP UDCG Controller
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To:     richard.yu@hpe.com, verdun@hpe.com, nick.hawkins@hpe.com,
        gregkh@linuxfoundation.org, robh+dt@kernel.org,
        krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org,
        linux-usb@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20230706215910.78772-1-richard.yu@hpe.com>
 <20230706215910.78772-2-richard.yu@hpe.com>
From:   Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
In-Reply-To: <20230706215910.78772-2-richard.yu@hpe.com>
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On 06/07/2023 23:59, richard.yu@hpe.com wrote:
> From: Richard Yu <richard.yu@hpe.com>
> 
> Provide access to the two register regions for GXP Virtual EHCI
> controller through the hpe,gxp-udcg binding.

Thank you for your patch. There is something to discuss/improve.

> 
> Signed-off-by: Richard Yu <richard.yu@hpe.com>
> ---
>  .../devicetree/bindings/usb/hpe,gxp-udcg.yaml | 70 +++++++++++++++++++
>  1 file changed, 70 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/usb/hpe,gxp-udcg.yaml
> 
> diff --git a/Documentation/devicetree/bindings/usb/hpe,gxp-udcg.yaml b/Documentation/devicetree/bindings/usb/hpe,gxp-udcg.yaml
> new file mode 100644
> index 000000000000..e6746374f97d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/usb/hpe,gxp-udcg.yaml
> @@ -0,0 +1,70 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/usb/hpe,gxp-udcg.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: HPE GXP USB Virtual EHCI controller

The word "virtual" in bindings pretty often raises questions, because we
describe usually real hardware, not virtual. Some explanation in
description would be useful.

> +
> +maintainers:
> +  - Nick Hawkins <nick.hawkins@hpe.com>
> +  - Richard Yu <richard.yu@hpe.com>
> +
> +description: |+

Drop |+

> +  The HPE GXP USB Virtual EHCI Controller implements 1 set of USB EHCI
> +  register and several sets of device and endpoint registers to support
> +  the virtual EHCI's downstream USB devices.
> +

If this is EHCI controller, then I would expect here reference to usb-hcd.

> +properties:
> +  compatible:
> +    enum:
> +      - hpe,gxp-udcg
> +
> +  reg:
> +    items:
> +      - description: UDC Global (UDCG) config controller
> +      - description: UDC Invidual config/interrupt controllers
> +
> +  reg-names:
> +    items:
> +      - const: udcg
> +      - const: udc
> +
> +  interrupts:
> +    maxItems: 1
> +
> +  hpe,vehci-downstream-ports:
> +    description: Number of downstream ports supported by the GXP

Why do you need this property in DT and what exactly does it represent?
You have one device - EHCI controller - and on some boards it is further
customized? Even though it is the same device?

> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    default: 4
> +    minimum: 1
> +    maximum: 8
> +
> +  hpe,vehci-generic-endpoints:
> +    description: Number of generic endpoints supported by the GXP
> +    $ref: /schemas/types.yaml#/definitions/uint32

Same concerns.

> +    default: 16
> +    minimum: 1
> +    maximum: 16
> +
> +required:
> +  - compatible
> +  - reg
> +  - reg-names
> +  - interrupts
> +  - hpe,vehci-downstream-ports
> +  - hpe,vehci-generic-endpoints
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    udcg@80400800 {

Node names should be generic. See also an explanation and list of
examples (not exhaustive) in DT specification:
https://devicetree-specification.readthedocs.io/en/latest/chapter2-devicetree-basics.html#generic-names-recommendation

Best regards,
Krzysztof