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

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Date:   Fri, 1 Apr 2022 10:34:02 +0530
From:   Aswath Govindraju <a-govindraju@...com>
To:     Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk@...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

Hi Rob,

On 01/04/22 05:50, Rob Herring wrote:
> On Thu, Mar 24, 2022 at 12:53:08PM +0100, Krzysztof Kozlowski wrote:
>> 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?
> 
> That's a simple question. Where does the ID GPIO signal go to? The 
> connector, so it goes in the connector node.
> 

Thank you for the clarification. Here ID-gpio is directly read by the
wrapper and hence, I have modeled it as a property in the wrapper dt
node. May I know if this wrong and should the modelling be looked at
differently?

Thanks,
Aswath

> If we have a driver for the usb-connector node, that's news to me. Not 
> that we couldn't, but that has nothing to do with designing the binding.
> 
> Rob