From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Stern Subject: Re: [patch update] Re: Run-time PM idea (was: Re: [RFC][PATCH 0/2] PM: Rearrange core suspend code) Date: Thu, 11 Jun 2009 14:36:30 -0400 (EDT) Message-ID: References: <200906111805.53388.oliver@neukum.org> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <200906111805.53388.oliver@neukum.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-pm-bounces@lists.linux-foundation.org Errors-To: linux-pm-bounces@lists.linux-foundation.org To: Oliver Neukum Cc: ACPI Devel Maling List , Linux-pm mailing list , LKML List-Id: linux-pm@vger.kernel.org On Thu, 11 Jun 2009, Oliver Neukum wrote: > Am Donnerstag, 11. Juni 2009 17:22:06 schrieb Alan Stern: > > > > Okay, I'll agree to that. =A0It should be made clear that a device = which > > > > is "suspended" according to this definition is not necessarily in a > > > > low-power state. =A0For example, before powering down the link to a= disk > > > > drive you might want the drive's suspend method to flush the drive's > > > > cache, but it wouldn't have to spin the drive down. > > > > > > This precludes handling busses that have low power states that are > > > left automatically. If such links are stacked the management of > > > acceptable latencies cannot be left to the busses. > > > An actual example are the link states of USB 3.0 > > > > I don't understand. =A0Can you explain more fully? > = > I am talking about the U1 and U2 feature of USB 3.0. > = > Or abstractly any power saving state that does autoresume in hardware. > In these cases you know that you can enter a powersaving state that > will add X latency. > = > In terms of user space API we'll probably add a way for user space > to specify how much latency may be added for power management's sake. > If busses are stacked the "latency budget" has to be handled at core leve= l. > If furthermore states that allow IO but with additional latency are ignor= ed, > the budget will be calculated wrongly. Okay, fine. What does this have to do with Rafael's work? Why does = setting the status to RPM_SUSPENDED even when a device is not in a = low-power state preclude handling buses that automatically change their = power state? I don't see any connection between Rafael's work and managing latencies, beyond the obvious fact that a device will have a higher latency when it is suspended than when it isn't. Alan Stern