Alan, will the 2.6.19-rc1 fix you mention also place USB controllers in D3 (after all the ports under them are in suspend) to save a bit of extra power? Nikos Kaburlasos -----Original Message----- From: Alan Stern [mailto:stern@xxxxxxxxxxxxxxxxxxx] Sent: Friday, October 13, 2006 7:19 AM To: Rafael J. Wysocki Cc: trenn@xxxxxxx; Kaburlasos, Nikos; linux-acpi@xxxxxxxxxxxxxxx Subject: Re: USB suspend/resume in linux On Fri, 13 Oct 2006, Rafael J. Wysocki wrote: > On Friday, 13 October 2006 10:39, Thomas Renninger wrote: > > On Thu, 2006-10-12 at 22:54 -0700, Kaburlasos, Nikos wrote: > > > Does anyone know whether the linux USB drivers support the suspend > > > feature on idle USB ports (i.e. the port has been idle for sometime and > > > so the driver transitions it in to a low-power 'suspend' state) while > > > the system is active and in S0 state? As far as I know, Windows don't > > > support that, I was wondering if linux does. > > > > > > Please note, I have no background on linux or in OS programming (I am a > > > hardware guy), so please be gentle with the level of technical detail in > > > your response :-) > > > > AFAIK linux is not doing that. > > Therefore the ohci (also uhci?) drivers need to poll the ports quite > > often even there is no device attached. This makes C-states less > > efficient (what should save more power than the suspended USB ports). I > > thought Windows is doing that, I at least heard Mac OS is doing it like > > that, but I don't know for sure. > > The proper solution to avoid polling should be to suspend idle ports, > > stop polling and wait for some kind of resume/attach event, but AFAIK > > nobody really works on that. Would be nice if someone gives this a > > try... > > Alan Stern has been working on USB autosuspend for quite some time > and there are some patches in -mm and in the recent mainline, AFAICT. Rafael is right. 2.6.19-rc1 already contains code that will suspend ports if the attached device doesn't have a driver. Under testing now is a patch to suspend ports when the attached device is idle, stop polling root-hub ports, and stop DMA activity (which is even worse than polling at keeping the processor out of low-power C states). Alan Stern - To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
