From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755699AbaEPUvM (ORCPT ); Fri, 16 May 2014 16:51:12 -0400 Received: from v094114.home.net.pl ([79.96.170.134]:63066 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752864AbaEPUvK (ORCPT ); Fri, 16 May 2014 16:51:10 -0400 From: "Rafael J. Wysocki" To: Jacob Pan Cc: Alan Stern , Linux PM list , ACPI Devel Maling List , Aaron Lu , Mika Westerberg , Linux Kernel Mailing List , Kevin Hilman , Ulf Hansson Subject: Re: [RFC][PATCH 2/3] PM / sleep: Mechanism to avoid resuming runtime-suspended devices unnecessarily Date: Fri, 16 May 2014 23:08:01 +0200 Message-ID: <1491497.iq6zE5EtMa@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/3.15.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: <20140516082055.40cd2bb4@ultegra> References: <20140515000320.3c1c9256@jacob-desktop> <20140516082055.40cd2bb4@ultegra> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday, May 16, 2014 08:20:55 AM Jacob Pan wrote: > On Thu, 15 May 2014 11:58:55 -0400 (EDT) > Alan Stern wrote: > > > On Thu, 15 May 2014, Jacob Pan wrote: > > > > > On Thu, 15 May 2014 10:29:42 -0400 (EDT) > > > Alan Stern wrote: > > > > > > > On Thu, 15 May 2014, Jacob Pan wrote: > > > > > > > > > > > should we respect ignore_children flag here? not all parent > > > > > > > devices create children with proper .prepare() function. > > > > > > > this allows parents override children. > > > > > > > I am looking at USB, a USB device could have logical > > > > > > > children such as ep_xx, they don't go through the same > > > > > > > subsystem .prepare(). > > > > > > > > > > > > Well, I'm not sure about that. Let me consider that for a > > > > > > while. > > > > > OK. let me be more clear about the situation i see in USB. > > > > > Correct me if I am wrong, a USB device will always has at least > > > > > one endpoint/ep_00 as a kid for control pipe, it is a logical > > > > > device. So when device_prepare() is called, its call back is > > > > > NULL which makes .direct_complete = 0. Since children device > > > > > suspend is called before parents, the parents .direct_complete > > > > > flag will always get cleared. > > > > > > > > > > What i am trying to achieve here is to see if we avoid resuming > > > > > built-in (hardwired connect_type) non-hub USB devices based on > > > > > this new patchset. E.g. we don't want to resume/suspend USB > > > > > camera every time in system suspend/resume cycle if they are > > > > > already rpm suspended. We can save ~100ms resume time for the > > > > > devices we have tested. > > > > > > > > This is a good point, but I don't think it is at all related to > > > > ignore_children. > > > > > > > > Instead, it seems that the best way to solve it would be to add a > > > > ->prepare() handler for usb_ep_device_type that would always turn > > > > on direct_complete. > > > > > > > yeah, that would solve the problem with EP device type. But what > > > about other subdevices. e.g. for USB camera, uvcvideo device? We > > > can add .prepare(return 1;) for each level but would it be better > > > to have a flag similar to ignore_children if not ignore_children > > > itself. > > > > Something like that could always be added. > or, how about if a device's .prepare() is NULL, we could > assume .direct_resume() should be set. i.e. You mean direct_complete (which is a flag, not a function), I suppose? Wouldn't that go a bit too far? It seems to be based on the assumption that all devices having no ->prepare() callback can be safely left in runtime suspend over a system suspend/resume cycle, but is that assumption actually satisfied for all such devices? > --- a/drivers/base/power/main.c > +++ b/drivers/base/power/main.c > @@ -1539,7 +1539,7 @@ static int device_prepare(struct device *dev, > pm_message_t state) pm_runtime_put(dev); > return ret; > } > - dev->power.direct_complete = ret > 0 && state.event == > PM_EVENT_SUSPEND > + dev->power.direct_complete = (!callback || ret > 0) && > state.event == PM_EVENT_SUSPEND && pm_runtime_suspended(dev); > dev_dbg(dev, "%s:direct_complete %d, info %s\n", __func__, > dev->power.direct_complete, info); > > > > > > Actually, I don't understand why this is not related to > > > ignore_children. Could you explain? > > > > It's hard to explain why two things are totally separate. Much > > better for you to describe why you think they _are_ related, so that > > I can explain how you are wrong. > > > > > If the parent knows it can ignore children and already rpm > > > suspended, why do we still ask children? > > > > The "ignore_children" flag doesn't mean that the parent can ignore > > its children. It means that the PM core is allowed to do a runtime > > suspend of the parent while leaving the children at full power. > > > > In particular, it doesn't mean that the children's ->suspend() > > callback will work correctly if it is called while the parent is > > runtime suspended. > that explains my question about ignore_chilren flag. thanks. > > > > Alan Stern > > > > [Jacob Pan] > -- > To unsubscribe from this list: send the line "unsubscribe linux-acpi" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.