Messages in this thread |  | | Date | Mon, 23 May 2011 12:28:27 -0400 (EDT) | | From | Alan Stern <> | | Subject | Re: [PATCH v12 7/8] usb: Adding SuperSpeed support to dummy_hcd |
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On Mon, 23 May 2011, Sarah Sharp wrote:
> > 2. whether the device HW supports SS protocol. In our scenario it can since > > SS support is enabled in our udc. (We haven't released it yet.) > > What is a UDC?
USB Device Controller. It's the device-side analog of a host controller.
> > Since in dummy_hcd all of this is much simpler I think that the device speed > > should be determined by driver->speed and "which type of cable the > > connection was made over - SS or HS". The "cable type" is exactly what the > > module parameter is. > > I really don't understand this. You're going to have a module parameter > for what type of cable is plugged in?
It would be more accurate to say the module parameter will be used to force the connection to run at a lower speed than the maximum possible. This is kind of like what happens when you plug in a SuperSpeed device using a USB-2 cable -- the connection runs at a lower speed than it could have.
> How can you tell which one the > user is going to use?
This isn't about actual cables or devices. dummy-hcd is an emulator; it presents as a host controller and a device controller both on the same system. This allows people to test gadget drivers without having any UDC hardware.
> What about the case where SuperSpeed enumeration > fails and you have to fall back to high speed?
If SuperSpeed enumeration fails, say because the device doesn't have any SuperSpeed descriptors, xhci-hcd doesn't fall back to high speed, does it? dummy-hcd should behave the same way.
> It seems like you really > need to handle both speeds and the speed fall back parameter in the same > driver. Isn't there some other gadget driver that has a fall back to > full or low speed when high speed enumeration fails?
That's a property of the gadget driver, not the UDC driver. dummy-hcd is a UDC driver (and an HCD too).
Alan Stern
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