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

[Sherry Sun]

Hi Vignesh,

> 
> 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?

I think we may not need to access OTG register if we add two subnodes for gadget and host.

But I see a for loop in dwc3_glue_bind() as follows, if there only one single node representing both Host and Device node under usb wrapper node, why we need this for loop?

212     for (node = fdt_first_subnode(fdt, dev_of_offset(parent)); node > 0;
213          node = fdt_next_subnode(fdt, node)) {

Best regards
Sherry sun

> 
> 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
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>>>>>>>> +	{ }
> >>>>>>>>>>>>> +};
> >>>>>> _______________________________________________
> >>>>>> U-Boot mailing list
> >>>>>> U-Boot at lists.denx.de
> >>>>>> https://l
> >>>>>>
> >>
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> >>
> >> --
> >> Regards
> >> Vignesh