> my understanding of c3 is that the process of gettting the
> cpu into c3 is
> completely independent of the system state (actually, usually
> performed when
> the system is full on). so the user thinks that the system is
> full-on (an
> has certain, reasonable expectations for responsivness) but
> the cpu can be
> cycling in an out of c3 with significant power savings while in c3.
Correct.
> if you have a 'sometimes busy' device, like a hid device
> (like a mouse or
> keyboard), suspending the usb to get the cpu into c3 won't
> work. the reason
> is kind of complicated to describe.
[snip]
You are absolutely right, that putting the HC into global suspend while
there are in-use devices on the bus is bad. I wouldn't make a case for that
- that's bad for reasons far bigger than C3. However, putting it into global
suspend when there are no connected devices should be OK.
C3 is only used on laptops. Laptops typically do not have USB devices hooked
up while on battery (e.g being used in an airport.) My point is that putting
the HC into global suspend *even in this narrow case* will be a big win.
This avoids all the gotchas you mentioned, and still improves the most
common laptop usage model.
It sounds like there are hub issues, but I have one, so I can test that
before sending out a patch.
Regards -- Andy
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