Messages in this thread | | | Date | Thu, 1 Jun 2006 09:43:27 -0700 | From | Greg KH <> | Subject | Re: [linux-usb-devel] Re: USB devices fail unnecessarily on unpowered hubs |
| |
On Thu, Jun 01, 2006 at 10:58:43AM -0400, Alan Stern wrote: > On Thu, 1 Jun 2006, Andrew Morton wrote: > > > On Thu, 01 Jun 2006 02:18:20 -0700 > > David Liontooth <liontooth@cogweb.net> wrote: > > > > > Starting with 2.6.16, some USB devices fail unnecessarily on unpowered > > > hubs. Alan Stern explains, > > > > > > "The idea is that the kernel now keeps track of USB power budgets. When a > > > bus-powered device requires more current than its upstream hub is capable > > > of providing, the kernel will not configure it. > > > > > > Computers' USB ports are capable of providing a full 500 mA, so devices > > > plugged directly into the computer will work okay. However unpowered hubs > > > can provide only 100 mA to each port. Some devices require (or claim they > > > require) more current than that. As a result, they don't get configured > > > when plugged into an unpowered hub." > > > > > > http://www.mail-archive.com/linux-usb-devel@lists.sourceforge.net/msg43480.html > > > > > > This is generating a lot of grief and appears to be unnecessarily > > > strict. Common USB sticks with a MaxPower value just above 100mA, for > > > instance, typically work fine on unpowered hubs supplying 100mA. > > > > > > Is a more user-friendly solution possible? Could the shortfall > > > information be passed to udev, which would allow rules to be written per > > > device? > > I'm not sure whether we create a udev event when a new USB device is > connected.
Yes we do. It's of the class "usb_device" and you can write a single udev rule to override the power test if you really want to.
Of course I don't recommend someone doing this, as it is violating the USB power rules, and it is a good thing that we are finally testing for them.
thanks,
greg k-h - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |