On Monday, 20 August 2007 22:19, Pavel Machek wrote:
> Hi!
>
> > > > > If I rmmod "ehci-hcd" then the power consumption is back to 69 W. This
> > > > > confirms that this is really USB-related. I have to admit that I did
> > > > > not expect an external drive to eat that much power from the system,
> > > > > especially when not used. I am told that VIA chips are notoriously bad
> > > > > at this kind of things. I'll try the same external drive on an Intel
> > > > > system later today.
> > > > >
> > > > > The last mystery remaining is how USB "activity" can cause my CPU to
> > > > > heat. I would expect the south bridge to heat, not the CPU.
> > > >
> > > > USB, or strictly speaking EHCI, OHCI and UHCI, use DMA. To allow
> > > > that the cache coherency logic has to be active. Therefore your CPU
> > > > cannot go to C3. Therefore it draws more power. The problem we are
> > > > facing in USB is that to get great savings, our coverage has to be perfect.
> > > > One device that cannot be autosuspended and we lose most savings.
> > >
> > > Ok.. but CONFIG_USB_SUSPEND should not really have anything to do with
> > > CONFIG_SUSPEND (= s2ram). Perhaps it should depend on CONFIG_PM
> > > instead?
> >
> > CONFIG_USB_SUSPEND doesn't depend on CONFIG_SUSPEND.
>
> Strange... what is going on here, then?
>
> config USB_SUSPEND
> bool "USB selective suspend/resume and wakeup (EXPERIMENTAL)"
> depends on USB && PM && EXPERIMENTAL
> help
> If you say Y here, you can use driver calls or the sysfs
> "power/state" file to suspend or resume individual USB
> peripherals.
>
> Also, USB "remote wakeup" signaling is supported, whereby
> some
> USB devices (like keyboards and network adapters) can wake
> up
> their parent hub. That wakeup cascades up the USB tree, and
> could wake the system from states like suspend-to-RAM.
>
> If you are unsure about this, say N here.
>
> config USB_OTG
> bool
> depends on USB && EXPERIMENTAL
> select USB_SUSPEND
> default n
>
> hmmm, it looks like USB_OTG can be selected without CONFIG_PM, but it
> selects USB_SUSPEND. Is that okay?
Well, I don't think so. It should depend on the same things as USB_SUSPEND,
IMO.
Greetings,
Rafael
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