Re: USB devices fail unnecessarily on unpowered hubs

[Pavel Machek]

Hi!

> 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."

Actually I have exactly opposite problem: my computer (spitz) can't
supply full 500mA on its root hub, and linux tries to power up
'hungry' devices, anyway, leading to very weird behaviour.

-- 
Thanks for all the (sleeping) penguins.
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