On Wed, May 13, 2020 at 9:09 PM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Wed, May 13, 2020 at 08:31:35PM +0200, Andrey Konovalov wrote: > > On Wed, May 13, 2020 at 8:14 PM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > On Wed, May 13, 2020 at 07:07:20PM +0200, Andrey Konovalov wrote: > > > > Hi Alan, > > > > > > > > I've been looking at this a little more. Do I understand correctly > > > > that even though Dummy UDC names endpoints as "ep1in", etc. it > > > > actually allows to assign endpoints addresses different from what is > > > > specified in the endpoint names (it uses find_endpoint() to find the > > > > right endpoint based on ep->desc)? E.g. you can technically assign > > > > endpoint with address 2 (| USB_DIR_IN) to "ep1in". > > > > > > Yes, that's right. In fact, you can do this with any UDC. (But with > > > other UDCs it won't work, whereas with dummy-hcd it will.) > > > > > > > If this is correct, this kind of limits Dummy UDC usage with Raw > > > > Gadget the way it is currently implemented, as Raw Gadget assumes that > > > > the endpoint address must be fixed when the endpoint is named as > > > > ep1in. > > > > > > Okay. That makes sense, since it is true for most UDCs. > > > > > > > Would it be acceptable to add another mode to Dummy UDC that names the > > > > endpoints as "ep-a"? Perhaps enabled with a module parameter. I'm not > > > > sure if this kind of naming would be technically correct, as "ep-a" > > > > name assumes that we can assign arbitrary transfer type to the > > > > endpoint as well, which isn't possible with Dummy UDC, as it doesn't > > > > support ISO transfers. > > > > > > > > Or do you think there can be another way to expose the fact that Dummy > > > > UDC allows arbitrary addresses? I could hardcode this into Raw Gadget, > > > > but it doesn't feel like the right approach. > > > > > > Why do you want to do this? Does anything go wrong if you just continue > > > to assume the endpoint numbers are fixed? > > > > Yes. Some USB drivers require endpoints with certain logical functions > > to have certain addresses (e.g. for ath9k: [1]). This limits the > > ability to use Raw Gadget + Dummy UDC for fuzzing, as sometimes we > > can't emulate such devices unless Dummy UDC endpoint with a particular > > address has required capabilities to implement those logical functions > > (e.g. for ath9k: we can't emulate USB_REG_IN_PIPE endpoint, as Dummy > > UDC only has an OUT endpoint with address 3). > > > > It's acceptable to be unable to emulate such devices with real UDCs > > with fixed address endpoints, but it would be highly desirable to be > > able to do that with Dummy UDC, as it technically supports > > configurable endpoint addresses. > > Okay, that's reasonable. > > > [1] https://elixir.bootlin.com/linux/v5.6.12/source/drivers/net/wireless/ath/ath9k/hif_usb.h#L68 > > > > > I suppose, if you thought this was really necessary, we could change > > > find_endpoint() so that it looks for a match against the endpoint's name > > > instead of against the address stored in the descriptor. > > > > That would make the behaviour of Dummy UDC match what is expected from > > it based on the endpoint names, but won't help with the problem > > described above. > > Would you want to do this anyway? It doesn't seem necessary to me. No, no need for this :) > > > > Or we could > > > change the last thirteen "generic" endpoints in ep_info[] to be > > > configurable: "ep-a", ..., "ep-m", or "ep-aout", ..., "ep-min". (The > > > fact that the endpoints don't support isochronous is exposed through the > > > usb_ep_caps structures.) > > > > I think this should work. If we put this under a module parameter, > > then we can make all endpoints have configurable names. > > No need for a module parameter; just make it a permanent change to the > driver. I was thinking that it could break some existing users, but I don't know for sure. > Would you like to submit a patch? Sure, will do. Thanks!
