linux-kernel - Re: [PATCH v2 1/2] dt-bindings: usb: Add documentation for AM62 USB Wrapper module

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Message-ID: <2b33798e-23c2-d4a5-171a-55c28bc40c40@kernel.org>
Date:   Thu, 24 Mar 2022 12:53:08 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Aswath Govindraju <a-govindraju@...com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-usb@...r.kernel.org, Felipe Balbi <balbi@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Roger Quadros <rogerq@...nel.org>,
        Vignesh Raghavendra <vigneshr@...com>,
        Kishon Vijay Abraham I <kishon@...com>
Subject: Re: [PATCH v2 1/2] dt-bindings: usb: Add documentation for AM62 USB
 Wrapper module

On 24/03/2022 12:40, Aswath Govindraju wrote:
> Hi Krzysztof,
> 
> On 24/03/22 16:37, Krzysztof Kozlowski wrote:
>> On 24/03/2022 08:34, Aswath Govindraju wrote:
>>> Add bindings for the TI's AM62 wrapper module for the Synopsys USBSS-DRD
>>> controller.
>>>
>>> Signed-off-by: Aswath Govindraju <a-govindraju@...com>
>>> ---
>>>
>>> Changes since v1:
>>> - made correction in grammer of clocks property description
>>>   and added maxItems in the interrupts property based on comments
>>>   received from Roger
>>> - corrected the title, fixed the description of
>>>   ti,syscon-phy-pll-refclk, added pattern properties and child node
>>>   in the example based on the comments from Krzysztof.
>>>
>>>  .../devicetree/bindings/usb/ti,am62-usb.yaml  | 117 ++++++++++++++++++
>>>  1 file changed, 117 insertions(+)
>>>  create mode 100644 Documentation/devicetree/bindings/usb/ti,am62-usb.yaml
>>>
>>> diff --git a/Documentation/devicetree/bindings/usb/ti,am62-usb.yaml b/Documentation/devicetree/bindings/usb/ti,am62-usb.yaml
>>> new file mode 100644
>>> index 000000000000..452bfdc6fb09
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/usb/ti,am62-usb.yaml
>>> @@ -0,0 +1,117 @@
>>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
>>> +%YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/usb/ti,am62-usb.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: TI's AM62 wrapper module for the Synopsys USBSS-DRD controller
>>> +
>>> +maintainers:
>>> +  - Aswath Govindraju <a-govindraju@...com>
>>> +
>>> +properties:
>>> +  compatible:
>>> +    const: ti,am62-usb
>>> +
>>> +  reg:
>>> +    maxItems: 1
>>> +
>>> +  ranges: true
>>> +
>>> +  power-domains:
>>> +    description:
>>> +      PM domain provider node and an args specifier containing
>>> +      the USB ISO device id value. See,
>>> +      Documentation/devicetree/bindings/soc/ti/sci-pm-domain.yaml
>>> +    maxItems: 1
>>> +
>>> +  clocks:
>>> +    description: Clock phandle to usb2_refclk
>>> +    maxItems: 1
>>> +
>>> +  clock-names:
>>> +    items:
>>> +      - const: ref
>>> +
>>> +  id-gpio:
>>> +    description:
>>> +      GPIO to be used as ID pin
>>> +    maxItems: 1
>>
>> I have doubts about this. If you USB controller handles the ID pin, then
>> probably this should be moved to usb-connector.yaml. I did not see
>> id-gpio in any other USB controller blocks.
>>
> 
> Yes, the USB wrapper handles the ID pin operation only. It also reads
> the status of VBUS by reading a register from its MMR and not using a
> gpio. After evaluating the role the based on the states if id pin and
> VBUS, this role is communicated to the dwc3 core driver using extcon.
> There is no way for the dwc3 driver to detect the role on its own.
> 
> 
> The usb-connector(drivers/usb/common/usb-conn-gpio.c) driver, seems to
> be implemented for driving the VBUS, based on ID and VBUS pin status.
> However, in case of the above implementation we need to communicate the
> detected role to the dwc3 core driver. Also, the wrapper does not
> control VBUS but it is the dwc3 core driver that drives the VBUS.
> Therefore, I think the usb-connector implementation cannot be used here.

I don't think about usb-conn-gpio.c but using the binding generic
binding for usb-X-connector and define a connector with ID.

Actually Rob could help here.

Rob,
Should the id-gpio be modeled as a property in this glue/wrapper driver
or rather as part of usb-connector child node?


Best regards,
Krzysztof