On Thu, 29 Nov 2007, Allardyce, Joel B. wrote: > Fellow Engineers, > > Is there any way to adjust the speed of one USB 2.0 device without > affecting other USB devices attached to the same Root Hub?
Yes. Provided the device you want to adjust is connected to a root hub and not an external hub. > I have a USB mass storage device that is USB 2.0 compatible. It > enumerates correctly, and generally works fine at High Speed (480 mbps). > > For a variety of EMI related reasons, I find that it is necessary for me > to run this device at Full Speed (12 mbps). In my application, speed is > not an issue, but EMI is. > > I know that the simple solution is to bind the UHCI driver to the Root > Hub, instead of the EHCI driver, but this has the unfortunate side > effect of forcing all USB devices to work in 1.1 mode. I would like to > avoid this since there is another USB mass storage device for which > there are no EMI issue that I would like to continue to run at High > Speed. > > I don't mind kernel hacking to get this to work, but I was hoping > someone out there already had a simple sysfs patch, or some such, that > would allow simple user space adjustment of a device's speed. > > To throw one more complication into the mix, I would, in the end, like > to find a way to force any device connected to a particular physical USB > port to run at Full Speed instead of High Speed. > > Note that I am running Debian Etch (kernel 2.6.18). If a feature like > this is already implemented in a later kernel, or one of the > experimental branches, then please let me know, and point out the > relevant source files. I could likely backport the changes as necessary > for my kernel. The feature was added in 2.6.21. The patch for it is here: http://marc.info/?l=linux-usb-devel&m=117089528503119&w=2 Most likely it will be easier for you to upgrade to a current kernel than to backport the patch. Alan Stern ------------------------------------------------------------------------- SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 _______________________________________________ Linux-usb-users@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-users
