On Jan 3, 2008 4:58 AM, Alan Stern <[EMAIL PROTECTED]> wrote: > On Wed, 2 Jan 2008, David Brownell wrote: > > > On Wednesday 02 January 2008, Alan Stern wrote: > > > On Wed, 2 Jan 2008, Mike Frysinger wrote: > > > > > > > perhaps the code size is arguable as to whether it really matters. > > > > the reason we want it is that we have a USB host controller that will > > > > not work with USB hubs, so we want to make sure the system does not > > > > attempt such things. (yes, such a USB host controller is retarded, > > > > but the decision was out of our hands.) > > > > > > Just out of curiosity, how does a host controller manage to avoid > > > working with external hubs? > > > > The transaction translators in external high speed hubs require > > hosts to issue particular USB transactions. If the host controller > > doesn't implement the that split transaction support, then it won't > > be supporting external hubs. > > So in theory one could connect a high-speed hub to such a host > controller and expect it to communicate with high-speed devices. So > long as no full- or low-speed devices are added there wouldn't be any > split transactions. It wouldn't be USB-2.0 compliant but it should > still work. >
Hmmm, basically, I think the answer is yes. But when you tell customers your devices support USB 2.0, they will try to plug-in lots of USB devices that you can not even imagine. If they plug-in a combo USB device including an external USB hub, the whole embedded Linux system maybe crash or hang there. So this patch is to refuse enumerate such unsupported USB devices. -Bryan Wu -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
