On Tue, 29 Jun 2004, Phil Brunner wrote: > >Right. A lot of devices aren't careful about sending too much data. They > >probably expect always to be asked for 192 bytes, which is what Windows > >does. > > > > > > > Since Windows asks for 192 bytes and most/all devices are designed to > work with Windows, it would probably be a good idea to ask for 192 bytes > by default for Linux USB. If this were done, then we could avoid the > case where a new/unrecognized device (such as my smartcard reader) > brings down the hub due to babble.
That's exactly what the patch we've been talking about does. > Perhaps we need a "whitelist" which > reduces length values for unambiguously identified devices to improve > efficiency? No need, the patch will do it for all USB devices (except those that already have a separate entry on the SCSI "blacklist".) > >What actuall can happen is a lot worse than that. USB host controllers > >made by VIA Technologies have a handy "feature" of shutting themselves off > >whenever they encounter "babble"! All it takes is one bad packet and > >that's it -- no more USB communications through that controller until it > >is fully reset. > > > >This problem doesn't arise under Windows. Apparently VIA's controller > >driver for Windows manages to turn off this shutdown feature. I sure > >would like to know how they do it! But VIA isn't talking. > > > > > From what you've told me, it sounds like Windows "turns off " the > shutdown feature by always requesting 192 bytes and avoiding the babble > entirely. No, that's wrong. The shutdown "feature" really does get turned off; I've tried it by running Windows and Linux on the same computer and attaching a USB gadget that I can force to generate a "babble" packet. With Linux the controller shuts down and with Windows it doesn't. Alan Stern ------------------------------------------------------- This SF.Net email sponsored by Black Hat Briefings & Training. Attend Black Hat Briefings & Training, Las Vegas July 24-29 - digital self defense, top technical experts, no vendor pitches, unmatched networking opportunities. Visit www.blackhat.com _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
