On Thu, 27 May 2004, Martin Diehl wrote: > Well, can we always trust the way how hubs report connect status and > changes? I think there is a race in the hub controller when detecting port > connection changes in parallel to ep0 status requests. To me it's not > clear from the usb specs whether there are timing requirements wrt. port > status requests. It's just speculation but what if we read the port > status faster than expected by the hub leading to some inconsistency?
Races and inconsistencies shouldn't matter. If the status changes at just about the same time as we read the status, it won't hurt anything if the change isn't reported until the _next_ time we read the status. And even if it is never reported at all, we'll be no worse off than we are now. As far as timing requirements... I don't know about any hubs in particular, but in general a USB device is expected to be able to handle a control request at any time, either by carrying it out or replying with NAK or STALL. Anyway, the current code already issues the status requests; my patch just changes the way we interpret the response. > Another race is due to the window between the point where the hub drivers > sees the connect-status-change bit set and the corresponding > clear-port-feature takes effect. If there is another bounce in this > window, we will not get another status change indication in the next > request, but the status might be changed (or not, if fast bounce+rebounce) > regardless. That race doesn't matter either. The code resets the counter to 0, so even if we did know there was a connect-status-change during that window we wouldn't have to do anything about it. Alan Stern ------------------------------------------------------- This SF.Net email is sponsored by: Oracle 10g Get certified on the hottest thing ever to hit the market... Oracle 10g. Take an Oracle 10g class now, and we'll give you the exam FREE. http://ads.osdn.com/?ad_id=3149&alloc_id=8166&op=click _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
