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

[Aswath Govindraju]

Hi Krzysztof, Rob,

On 01/04/22 13:19, Krzysztof Kozlowski wrote:
> 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@xxxxxx>
>>>>>>> ---
>>>>>>>
>>>>>>> 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@xxxxxx>
>>>>>>> +
>>>>>>> +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?
> 
> 

Thank you for clarification. Now I understood, I was looking at it in
the wrong way and when looking at in in terms hardware I understood the
mistake that I have been doing. So, the id-gpio is actually not an
inherent part of the wrapper but rather something that it gets from the
connector. So, there needs to be different node describing this.

Thanks,
Aswath

> Best regards,
> Krzysztof