On Wed, 12 Oct 2005, David Brownell wrote: > Potentially; the usb_get_urb() and atomic_inc() should be paired with the > list_add_tail() -- under spinlock protection -- rather than being done as > late as it's now done by hcd_submit_urb(). That's what Alan's patch does. > > Similarly, the urb->*_dma fields should be set up before list_add_tail(), > at least for urbs not going to the root hub. Of course that won't matter > for non-DMA HCDs like sl811. > > Root hub urbs could stand a closer look; now that they have a real > queue, usbcore shouldn't need to use an hcd->status_urb any more. > (Limiting them to single entry queues ...) > > The sl811 code should probably refuse to start() urbs it hasn't marked > yet (by setting urb->hcpriv) too. There's no point to maintaining a > parallel queue for each endpoint, but it should still ignore URBs that > haven't yet been set up both by usbcore and by the HCD. And setting > hcpriv is what marks the URB as having been set up by that HCD.
If every HCD is careful not to use URBs that aren't marked (i.e., for which urb->hcpriv is NULL), then a single endpoint queue would be okay. And it wouldn't be necessary to move the usb_get_urb and atomic_inc statements either (or the DMA stuff). We will still have the problem that the HCDs don't have access to the spinlock that protects the queue pointers. I suppose the spinlock could be EXPORTed. Alan Stern ------------------------------------------------------- This SF.Net email is sponsored by: Power Architecture Resource Center: Free content, downloads, discussions, and more. http://solutions.newsforge.com/ibmarch.tmpl _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
