On Sun, 10 Jun 2007, Oliver Neukum wrote: > Am Sonntag, 10. Juni 2007 schrieb Alan Stern: > > On Sun, 10 Jun 2007, Oliver Neukum wrote: > > > > > Am Sonntag, 10. Juni 2007 schrieb Greg KH: > > > > > Yes, it could be done that way, I think. It'll take more work than a > > > > > simple search-and-replace. The trickiest part is how to unlink an > > > > > URB > > > > > after it has been submitted but before it has been handed to the > > > > > HCD... > > > > > > > > We allow that today? How, multiple threads doing the submit and then > > > > unlink call? That's looney. We should not worry about that until after > > > > > > Isn't that exactly what a resubmission in the completion handler is? > > > > No. It may be similar in some vague sense but it's not the same thing > > at all. What Greg and I are talking about is this: > > > > CPU 0 CPU 1 > > ----- ----- > > call usb_submit_urb > > call usb_unlink_urb > > call hcd->driver->urb_enqueue > > > > What you're talking about is this: > > > > CPU 0 > > ----- > > call usb_hcd_giveback_urb > > call urb->complete > > call usb_submit_urb > > > > It doesn't involve multiple threads or unlinking. > > But suppose you want to unlink an URB that is resubmitted in its completion > handler. I see no way to avoid hitting that window. Unless you want to force > drivers to use synchronization. At least usb_kill_urb() has to always work.
If you don't use usb_kill_urb or some sort of synchronization, then there's not much point in unlinking an URB that is resubmitted by its completion handler. After all, you run the risk of calling usb_unlink_urb just before the handler has resubmitted it. However you are correct that the scenario I described can easily arise with usb_kill_urb, so it does need to be handled correctly. It's not looney after all! Alan Stern ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
