On Tue, 8 May 2007, David Brownell wrote: > > > > It's probably nothing, but this line in ohci-q.c in td_submit_urb raised > > > an eyebrow: > > > > > > urb_priv->ed->hwHeadP &= ~cpu_to_hc32 (ohci, ED_C); > > > > > > There is a comment "resetting toggle is meaningless if the endpoint is > > > active" above this code. While that's true, I wouldn't expect this > > > operation to be atomic. What happens if the HC is updating headP during > > > this block? > > It's not allowed to be active at that point. The flag being > tested is set only by usb_clear_halt()
More accurately, the flag being tested (i.e., the toggle value) is _cleared_ only by usb_clear_halt() and usb_enable_endpoint(). ohci-hcd sets the toggle in the next line, and it remains set until the endpoint is cleared or re-enabled. > ... for OHCI and any > other HCD managing toggle in hardware, the software flag which > must have been set before that condition triggers (and that > statement executes) is only used to say "reset this endpoint's > toggle, whatever it may be". Got it. Thank you. 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
