[LAU] USB on ThinkPad T520

Monty Montgomery xiphmont at gmail.com
Sun May 13 20:40:28 UTC 2012

On Sun, May 13, 2012 at 4:06 PM, Robin Gareus <robin at gareus.org> wrote:

> Any hints on how to address this issue, then? If I understand correctly,
> new USB2-class-compliant devices are not an issue, but on modern
> machines with only EHCI, USB1-class-compliant devices may or may not
> work... right?

The primary problem with EHCI is only bandwidth allocation; it's
inefficient.  I'm unaware of any timing problems.  That's not to say
they don't exist, I just haven't run into them myself.

Poor bandwidth efficiency aside, I usually see ~ the same latency and
timing behavior on UHCi and EHCI with a TT.

> Would forward porting your schedulers be an option? Has anything of this
> been merged into recent kernels?

I'm unlikely to do this unless I need it myself, sorry :-(.  Not
enough time, too much to do.  And the kernel devs are absolutely right
that replacing a working but inefficient driver with a brand new one
that is faster but will require long-term testing is not something to
be done lightly.

> Maybe you can do play some tricks on the EHCI controller/scheduler: add
> an old USB1.1 hub in between the soundcard and the PC... but that's just
> a shot in the dark.

You'll still be going through the translator in the root hub.


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