Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753087AbaFPDDV (ORCPT ); Sun, 15 Jun 2014 23:03:21 -0400 Received: from hqemgate15.nvidia.com ([216.228.121.64]:16149 "EHLO hqemgate15.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752012AbaFPDDT convert rfc822-to-8bit (ORCPT ); Sun, 15 Jun 2014 23:03:19 -0400 X-PGP-Universal: processed; by hqnvupgp08.nvidia.com on Sun, 15 Jun 2014 19:57:47 -0700 From: Allen Yu To: Alan Stern CC: "Rafael J. Wysocki" , Pavel Machek , "Len Brown" , Greg Kroah-Hartman , "linux-pm@vger.kernel.org" , "linux-kernel@vger.kernel.org" Date: Mon, 16 Jun 2014 11:03:02 +0800 Subject: RE: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled and device suspended. Thread-Topic: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled and device suspended. Thread-Index: Ac+H3Xae0S68LLvuTGuWvxLUEw87XgBL0IfQ Message-ID: <9E7892CE01168A46922BCCE04DB02F9828E62353@HKMAIL01.nvidia.com> References: <1402740209-16432-1-git-send-email-alleny@nvidia.com> In-Reply-To: Accept-Language: zh-CN, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: zh-CN, en-US MIME-Version: 1.0 Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 14 Jun 2014, Alan Stern wrote: > > dev->power.is_suspended is set after core suspends device during system > suspend. > > This flag mostly means device is not operational (all I/O been > > quiesced, no more data read or write acceptible, etc.), hence it's > > dangerous to access hardware if device is suspended even though runtime > PM status is RPM_ACTIVE. > > > > In turn, we should allow device to be accessed in case device is *not* > > suspended and runtime PM status is RPM_ACTIVE, even if runtime PM > > disabled. This corner case can happen to a device in a generic PM > > domain if the domain is not powered off while preparing for a system-wide > power transition. > > I don't understand. Even if the PM domain isn't powered off, the device's > is_suspended flag will still be set by __device_suspend(). Yes, is_suspended flag will be set by __device_suspend(). But runtime PM can be disabled in pm_genpd_prepare(): 914 static int pm_genpd_prepare(struct device *dev){ ... 956 /* 957 * The PM domain must be in the GPD_STATE_ACTIVE state at this point, 958 * so pm_genpd_poweron() will return immediately, but if the device 959 * is suspended (e.g. it's been stopped by genpd_stop_dev()), we need 960 * to make it operational. 961 */ 962 pm_runtime_resume(dev); 963 __pm_runtime_disable(dev, false); ... 978 } And there is a gap between pm_genpd_prepare() and __device_suspend(), during which is_suspended flag is *not* yet set but runtime PM is disabled and device status is RPM_ACTIVE. > > > In this case, runtime PM status will > > be set to RPM_ACTIVE and then runtime PM is disabled. After that, > > device driver may call pm_runtime_get_sync() and rpm_resume() should > > return 1, because the device is still active as long as not been suspended. > > Isn't that what the existing code does already? Your patch seems to change > it so that it _doesn't_ behave the way you want. > The existing code return 1 for case is_suspended flag is set. That means __device_suspend() has been called and device is not in operational state. Whereas the case I mentioned above is before device is suspended. It's dangerous to access device if it's in suspended state, so I propose only allowing access to a device if it's not suspended (i.e. value of "is_suspneded" flag is false). > > Signed-off-by: Allen Yu > > --- > > drivers/base/power/runtime.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/base/power/runtime.c > > b/drivers/base/power/runtime.c index 67c7938..39885f1 100644 > > --- a/drivers/base/power/runtime.c > > +++ b/drivers/base/power/runtime.c > > @@ -608,7 +608,7 @@ static int rpm_resume(struct device *dev, int > rpmflags) > > repeat: > > if (dev->power.runtime_error) > > retval = -EINVAL; > > - else if (dev->power.disable_depth == 1 && dev- > >power.is_suspended > > + else if (dev->power.disable_depth == 1 && !dev- > >power.is_suspended > > && dev->power.runtime_status == RPM_ACTIVE) > > retval = 1; > > Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/