linux-kernel - Re: [PATCH RESEND 1/7] dt-bindings: misc: add schema for USB hub on Kirin devices

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Date:   Thu, 16 Dec 2021 13:52:01 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc:     Wei Xu <xuwei5@...ilicon.com>, Yu Chen <chenyu56@...wei.com>,
        John Stultz <john.stultz@...aro.org>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND 1/7] dt-bindings: misc: add schema for USB hub on
 Kirin devices

On Wed, Dec 15, 2021 at 2:54 AM Mauro Carvalho Chehab
<mchehab+huawei@...nel.org> wrote:
>
> From: Yu Chen <chenyu56@...wei.com>
>
> This patch adds binding documentation to support USB HUB and
> USB data role switch of HiSilicon HiKey960 and HiKey970 boards.

I don't see the point in reviewing this given a driver was already
merged anyways, I can't imagine that plugging in one USB port causing
others to disconnect is a USB compliant design, and there are few
boards and fewer users that care.

> [mchehab: updated OF schema and added HiKey970 example]
> Signed-off-by: Yu Chen <chenyu56@...wei.com>
> Signed-off-by: John Stultz <john.stultz@...aro.org>
> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
> ---
>
> To avoid mailbombing on a large number of people, only mailing lists were C/C on the cover.
> See [PATCH RESEND 0/7] at: https://lore.kernel.org/all/cover.1639558366.git.mchehab+huawei@kernel.org/
>
>  .../bindings/misc/hisilicon,hikey-usb.yaml    | 87 +++++++++++++++++++
>  1 file changed, 87 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/misc/hisilicon,hikey-usb.yaml
>
> diff --git a/Documentation/devicetree/bindings/misc/hisilicon,hikey-usb.yaml b/Documentation/devicetree/bindings/misc/hisilicon,hikey-usb.yaml
> new file mode 100644
> index 000000000000..761ab686121a
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/misc/hisilicon,hikey-usb.yaml
> @@ -0,0 +1,87 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +# Copyright 2019 Linaro Ltd.
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/misc/hisilicon,hikey-usb.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: HiKey960/970 onboard USB GPIO Hub
> +
> +maintainers:
> +  - John Stultz <john.stultz@...aro.org>
> +
> +description: |
> +  Supports the onboard USB GPIO hubs found on HiKey960/970.
> +  Such hubs require a power supply for the USB I/O. Depending on the
> +  exact hub model, after USB I/O is powered up, a reset should be needed.
> +
> +  It also acts as a role-switch intermediary to detect the state of
> +  the USB-C port, to switch the hub into dual-role USB-C or host mode,
> +  which enables and powers up the onboard USB-A host ports.
> +
> +  Schematics about such hubs can be found here:
> +    https://github.com/96boards/documentation/raw/master/consumer/hikey/hikey960/hardware-docs/HiKey960_Schematics.pdf
> +    https://www.96boards.org/documentation/consumer/hikey/hikey970/hardware-docs/files/hikey970-schematics.pdf
> +
> +properties:
> +  compatible:
> +    enum:
> +      - hisilicon,usbhub
> +
> +  typec-vbus-gpios:
> +    $ref: /schemas/types.yaml#/definitions/phandle-array
> +    description: phandle to the typec-vbus gpio
> +
> +  otg-switch-gpios:
> +    $ref: /schemas/types.yaml#/definitions/phandle-array
> +    description: phandle to the otg-switch gpio
> +
> +  hub-reset-en-gpios:
> +    $ref: /schemas/types.yaml#/definitions/phandle-array
> +    description: phandle to the hub reset gpio
> +
> +  usb-role-switch:
> +    $ref: /schemas/types.yaml#/definitions/flag
> +    description: Support role switch.
> +
> +  hub-vdd-supply:
> +    description: regulator for hub power
> +
> +  port:
> +    description: |
> +      describe hadware connections between USB endpoints.

USB endpoints? That's a s/w construct.

> +      Two ports are supported: the first being the endpoint that will

'port' means exactly 1 port.

> +      be notified by this driver, and the second being the endpoint
> +      that notifies this driver of a role switch.

IMO, this node should represent the HS switch. I would expect an input
port connected to the USB host and an output port with 2 endpoints
connected to USB-C connector and the hub.

host(HS port) -> (port@0)Switch(port@1)+--endpoint@0 -> USB-C connector
                                       |--endpoint@1 -> 2.0 hub

Then there's what does the hub look like which has been discussed
separately and is still not upstream I think.

But again, given this is devboard with limited use, I would just make
using USB-C vs. USB host connectors a fixed boot time configuration
with some one time setup and move on...

Rob