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    SubjectRe: USB devices fail unnecessarily on unpowered hubs
    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?
    >

    (added linux-usb cc)

    Yes, it sounds like we're being non-real-worldly here. This change
    apparently broke things. Did it actually fix anything as well?
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