Messages in this thread | | | Date | Thu, 19 Mar 2015 10:17:46 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [RFC][PATCH 1/9] usb: hcd: Introduce usb_start/stop_hcd() |
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On Thu, 19 Mar 2015, Roger Quadros wrote:
> > It would be a lot simpler to unbind the host controller driver > > completely when switching to device mode and rebind it when switching > > back. I guess that is the sort of heavy-duty approach you want to > > avoid, but it may be the only practical way forward. > > So you mean directly calling usb_add/remove_hcd() from the OTG core?
Well, actually I meant calling device_release_driver() and driver_probe_device(). But usb_add/remove_hcd() might work just about as well, although I think some of the HCDs may still require a little rewriting. Peter Chen says it works for Chipidea.
> I don't see any issues with that other than it being a heavy-duty operation > like you said and hope that it doesn't violate the OTG spec timing.
The timing is a tough issue. I'm not sure what we can do about it, though.
> Looking at Figure 5-3: "HNP Sequence of Events (FS)" of the OTG 2.0 spec > we have about 150ms (X10) to switch from B-Device detected A connect (b_wait_acon state) > to driving bus reset (b_host state). I don't think this should be an issue in modern SoCs > but I'm not very sure. > > In any case I can migrate to the add/remove hcd approach to simplify things.
Good luck.
Alan Stern
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