[U-Boot] [PATCH v4 2/4] USB: host: Add the USB3 host driver

[Vignesh Raghavendra]

Hi Sherry,

[...]
>> AFAIK, U-Boot does not support runtime switching of USB port to host from
>> device and vice versa. This is the case for existing driver like DWC3/MUSB etc.
>>
>> Ideally we would need a role switch driver that unbinds and rebinds host vs
>> device driver as when required based on U-Boot cmd or via an API (if
>> required to be done during SPL stage etc).
> 
> I wonder if we can add two subnodes under the wrapper node as below, one bind to usb gadget driver and another bind to usb host driver.
> So if we want to use usb device, just call the gadget driver, and if want to use usb host, just call the host driver. The driver will probe correspond node.
> I'm not sure if it is feasible, what do you think about it?
> 
>       usbss0: cdns_usb at 4104000 {
>           compatible = "ti,j721e-usb";
>           [....]
>           usb0: usb at 6010000 {		/* xhci reg address*/
>               compatible = "cdns,usb3-1.0.1";
> 	dr_mode = "host";
> 	[....]
> 	}
>           usb1: usb at 6020000 {		/* dev reg address*/
>               compatible = "cdns,usb3-1.0.1";
> 	dr_mode = "peripheral";
> 	[....]
> 	}
>     }
> 

But this is not how DT would look in kernel. There will be single DT
node representing both Host and Device node. DT repesentation should not
be changed based on OS/bootloader, its HW description and must remain same.
Unbinding host/gadget driver and rebinding with a different role should
not be hard as the U-Boot core infrastructure exists.

Moreover if xhci reg and dev reg are separated into different nodes dont
we still need access to OTG register block to switch b/w host and device
mode?

Regards
Vignesh

> Best regards
> Sherry sun
> 
>>
>> Regards
>> Vignesh
>>
>>> Best regards
>>> Sherry sun
>>>
>>>>
>>>> JJ
>>>>
>>>>>> Then when binding the wrapper node, it will hard-coded the two
>>>> subnodes
>>>>>> to different driver(gadge/host driver) according to the dr_mode
>>>>>> property
>>>> in
>>>>>> nodes.
>>>>>>
>>>>> Do you think I understand it right?
>>>>
>>>>>
>>>>> Best regards
>>>>> Sherry sun
>>>>>
>>>>>> Best regards
>>>>>> Sherry sun
>>>>>>
>>>>>>> JJ
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>>>>>> +	{ }
>>>>>>>>>>>>> +};
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>> --
>> Regards
>> Vignesh