[lkml]   [2006]   [Jun]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: USB devices fail unnecessarily on unpowered hubs

> 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.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2006-06-03 09:16    [W:0.129 / U:0.156 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site