On Wed, Apr 26, 2006 at 04:07:29PM -0400, Alan Stern wrote: > On Wed, 26 Apr 2006, Greg KH wrote: > > > On Wed, Apr 26, 2006 at 11:32:06AM -0400, Alan Stern wrote: > > > I've seen a couple of bug reports which boiled down to the fact that the > > > hub driver doesn't enable port power if the hub descriptor indicates the > > > port power isn't switchable (a la USB 1.0). > > > > 1.0 USB Hubs? They should be thrown away, due to all of the problems in > > them. 1.1 fixed a bunch of bugs in USB hubs for this very reason. I > > have only seen one 1.0 hub, and that was a pre-production version. > > > > Also, those hubs should be very old, are we sure we want to support > > them? Windows shouldn't :) > > These are not USB 1.0 hubs; they are more recent than that!
Ah, ok, I thought you were referring to 1.0 hubs above. > The problem is that in their hub descriptors, the Logical Power Switching > Mode (LPSM) (part of wHubCharacteristics) is set to 3. According to the > USB 2.0 spec, that means: > > Reserved. Used only on 1.0 compliant hubs that implement no power > switching. > > Possibly because they do this because they only emulate power switching > and don't implement it fully. > > In fact, lots of hubs don't implement port power switching. Even when > they say that power is turned off to some port, all they really mean is > that they will ignore any events on that port -- but the power is still > on. Relatively few brands of hubs truly do switch the power. > > (This has caused difficulties for people who want to use USB bus power as > a low-cost GPIO signal. They had to try a bunch of different brands > before finding some that worked.) Heh, I hadn't heard of people doing that before, that's funny. Anyway, I don't have a problem with this change. thanks, greg k-h ------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
