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SubjectRe: [RFC/PATCH 2/2] usb: Adding SuperSpeed support to dummy_hcd
On Tue, Oct 12, 2010 at 09:55:29AM -0400, Alan Stern wrote:
> On Tue, 12 Oct 2010, Brokhman Tatyana wrote:
>
> > Hi Alan
> >
> > Thanks you for your comments. Please see my reply inline.
>
> > > In addition, I suspect the dummy_hcd driver structure shouldn't contain
> > > an address_device entry. It should be present only in dummy_ss_hcd.
> >
> > I'm not sure I follow...
> > According to the code and comments in hub.c address_device cb is used if
> > the host controller wishes to choose the device address itself instead of
> > the address chosen by the core.
>
> Correct.
>
> > It seems to me that there is nothing
> > preventing the dummy_hcd from supplying such cb as well. Is there?
> > Having both HS and SS dummy_hcd determine the device address seems more
> > convenient for testing proposes.
>
> For testing purposes, it is best to imitate the behavior of a real
> device as closely as possible. USB-2.0 host controllers do not assign
> their own addresses to devices; they use the addresses provided by
> usbcore. I think this is also true for the low/full/high-speed
> components of a USB-3.0 controller.

There is only one controller, the xHCI controller, that handles all
device speeds. There are no companion controllers for a USB 3.0 host
controller. The xHCI host controller uses the hardware assigned address
for all devices (LS/FS/HS/SS), not the usbcore address.

But I'll admit I don't understand what dummy-hcd is supposed to do, so
I'm a bit confused as to why it needs an address_device function. Is it
supposed to be the gadget-side interface to the hardware that's
transmitting over USB (i.e. responding to the USB host)? Or does it
have something to do with a gadget switching over to host mode for OTG?

Sarah Sharp


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