[Fwd: Re: EHCI and OHCI drivers & OLPC]

[Jim Gettys]

Here's some interesting information from David Brownell, one of the USB
driver maintainers.
                             - Jim


On Thursday 26 October 2006 11:46 am, David Brownell wrote:
> On Thursday 26 October 2006 5:47 am, you wrote:
> > As you may know, USB (and SD) are the buss(s) supported by our
machine,
> > and therefore your work is integral to our system.

By the way, FWIW you might care that

 (a) the OHCI driver should already be quite power-efficient, and it
     gets run regularly on embedded ARMs where that matters a lot.

 (b) the EHCI driver is surely less efficient, though at least it's
     good about avoiding needless DMA.

 (c) 2.6.19 includes some new mechanisms under CONFIG_USB_SUSPEND that
     change the equations a bit, eventually adding up to improvements
     but possibly causing minor PM regressions meanwhile.

For USB there are basically two configs where PM can improve things.
One is "nothing connected"; there, EHCI can improve but OHCI can't.
The other is where an intermittently-used device is connected, like
a mouse, and that's where the 2.6.19 "autosuspend" mechanisms will
eventually be helping with across-the-board improvement.

- Dave


-- 
Jim Gettys
One Laptop Per Child