Hi, Benjamin Herrenschmidt <benh@xxxxxxxxxxx> writes: > On Sat, 2018-06-23 at 11:07 -0400, Alan Stern wrote: >> On Sat, 23 Jun 2018, Benjamin Herrenschmidt wrote: >> >> > Hi folks ! >> > >> > I noticed some UDC drivers setup a "desc" pointer for ep0.desc for the >> > driver, some don't. >> > >> > Is it officially needed ? >> >> No, it isn't. The only "core" routine that requires a desc pointer in >> the endpoint structure is usb_ep_enable, and that routine explicitly >> says it may not be called for ep0. >> >> > Additionally some UCDs NULL out the desc pointer in ep_disable, is that >> > also a requirement ? >> >> No. A disabled endpoint doesn't have any requirements on its >> descriptor or lack thereof. >> >> > I somewhat fear that if somebody calls stuff like usb_ep_align() on ep0 >> > it will crash without a valid desc pointer... >> >> That would be a pretty strange thing to do. I'd say it's not worth >> worrying about until somebody makes that mistake. > > Well, things like usb_endpoint_maxp() seem not *completely* far fetched > but yeah EP0 is usually special enough that it should be ok. That said, > I noticed some UDC drivers to setup a dummy desc there so I was > wondering ... dwc3 does that, but it's really just for convenience. It was easier to have the descriptor and share the biggest part of the code for the code of a tiny little descriptor data. -- balbi
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