Am Saturday 17 January 2009 23:44:12 schrieb David Brownell: > On Saturday 17 January 2009, Oliver Neukum wrote: > > > > > What HCD change(s) were you thinking of? > > > > HCDs shall not call the completion handler from the context that > > called usb_submit_urb(), if necessary from a workqueue. > > That wouldn't address $SUBJECT **at all** ... the issue is > calling completions from the context issuing usb_unlink_urb(). Yes, you are right. ALthough the same problem arises. > Phasing in such a context restriction could be problematic, > and of course there's the issue of actually getting and testing > patches for all the relevant HCDs. Could usbcore at least > detect that an HCD isn't adhering to such new rule? Is it really new? It seems to me the behavior was never defined, but the big three behave this way. > There's a complementary issue ... a completion callback may > call usb_unlink_urb(). I'd have to think more about that, > but be very cautious about changing _those_ semantics. On > fault paths, a completion callback must be able to unlink > every URB in the queue for its endpoint, without letting > any of them hit the hardware. Yes. > Last time I thought about this issue, I kept thinking that > what's *really* needed is getting rid of one-at-a-time > semantics for unlinking URBs ... and replacing them with > "unlink everything queued to this endpoint" semantics. Endpoint 0 is shared. You cannot let one driver massacre everything. > I don't recall even one case where "dequeue just one URB" > was really the desired usage model. It's a leftover from > the early USB work for the Linux 2.2.8+ kernel. > > > > Do you know which HCDs are affected? > > The unlinking issue generally applies to any HCD that > doesn't have to disable hardware queues to unlink. > It's the "disable queue" which forces a contex switch > on stuff like EHCI/OHCI/UHCI, so they don't see $SUBJECT. > > Right off the top of my head: sl811_hc and musb_hdrc > both have purely software queues, and can (do!) process > unlinks immediatly. Plus there's the HCD associated > with the $SUBJECT bug report ... ISTR seeing a comment > from Jeremy about other affected HCDs. OK, if we are talking API changes, do we really want a callback if the hardware never saw an URB? Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
