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 09:49:36 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Aswath Govindraju <a-govindraju@...com>,
        Rob Herring <robh@...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 01/04/2022 07:04, Aswath Govindraju wrote:
> 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?

What do you mean here by "read"? If you refer to the driver reading the
pin value, it is less related to the hardware, right?


Best regards,
Krzysztof