suspend/resume timings

[Chris Ball]

On Tue, Apr 03, 2007 at 08:52:26AM -0700, Hal Murray wrote:
> What's the plan for USB?  Currently it gets powered off.  Is that the long 
> term plan?  If so, we can't wakeup the CPU from USB gizmos.
> 
> USB is polled from the host.  (There isn't a separate interrupt wire.)  Does 
> the XO have special hardware to do that or does the CPU need to poke the 
> hardware occasionally?
> 
> What's the short/intermediate plan for people using ssh over a USB Ethernet 
> dongle?

There are several possible strategies:

   * not supporting USB at all while asleep
   * not *going* to sleep when USB is being used
   * going to sleep only if that particular USB device is incapable 
     of creating events that would require you to wake up (such as a
     USB hard disk) and not sleeping if it is capable (such as a USB
     ethernet dongle).

Jordan had some crafty ideas about getting dynticks involved in all
this yesterday on IRC, such as only sleeping when you know you won't
be woken up by software in the next second -- with dynticks we know
when the next software wakeup is.  Of course, that leaves hardware
interrupts..

As you can see, we've only just started thinking about this.  Ideas
welcome.

- Chris.
-- 
Chris Ball   <cjb at laptop.org>