Re: Fwd: USB suspending

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Fri, 5 Oct 2007, Oliver Neukum wrote:

> Am Freitag 05 Oktober 2007 schrieb Rafael J. Wysocki:
> > Hi,
> > 
> > Below is a Lukas' question related to USB suspend that I'm not able to answer.
> > 
> > Please help!
> > 
> > Greetings,
> > Rafael
> > 
> > 
> > ----------  Forwarded Message  ----------
> > 
> > Subject: USB suspending
> > Date: Friday, 5 October 2007 14:54
> > From: Lukas Hejtmanek <xhejtman@xxxxxxxxxxx>
> > To: "Rafael J. Wysocki" <rjw@xxxxxxx>
> > 
> > Hello,
> > 
> > I've noticed that while suspended in RAM USB ports are powered so any device
> > connected to the port gets power. Can I turn off power of all USBs ports while
> > suspending to RAM?
> 
> If you do that all devices on these ports will be disconnected.
> If you still insist on doing so, it is done by a USB control request.

No it isn't.  In fact, I think it can't be done at all.  For example,
many USB controllers don't support PCI power management.  None of the
controllers on regular desktop and laptop machines support port-power
switching.

> But power consumption on these ports is minimal for suspended devices,
> so it is a bad idea.

Right.  Power consumption is even smaller on ports with no devices 
plugged in.

Alan Stern


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