linux-kernel - Re: [PATCH AUTOSEL 4.14 15/31] PCI: PM: Avoid possible suspend-to-idle issue

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Message-ID: <20190619210124.GF2226@sasha-vm>
Date:   Wed, 19 Jun 2019 17:01:24 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Keith Busch <keith.busch@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 4.14 15/31] PCI: PM: Avoid possible
 suspend-to-idle issue

On Tue, Jun 11, 2019 at 05:25:48PM +0200, Rafael J. Wysocki wrote:
>On 6/8/2019 1:46 PM, Sasha Levin wrote:
>>From: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
>>
>>[ Upstream commit d491f2b75237ef37d8867830ab7fad8d9659e853 ]
>>
>>If a PCI driver leaves the device handled by it in D0 and calls
>>pci_save_state() on the device in its ->suspend() or ->suspend_late()
>>callback, it can expect the device to stay in D0 over the whole
>>s2idle cycle.  However, that may not be the case if there is a
>>spurious wakeup while the system is suspended, because in that case
>>pci_pm_suspend_noirq() will run again after pci_pm_resume_noirq()
>>which calls pci_restore_state(), via pci_pm_default_resume_early(),
>>so state_saved is cleared and the second iteration of
>>pci_pm_suspend_noirq() will invoke pci_prepare_to_sleep() which
>>may change the power state of the device.
>>
>>To avoid that, add a new internal flag, skip_bus_pm, that will be set
>>by pci_pm_suspend_noirq() when it runs for the first time during the
>>given system suspend-resume cycle if the state of the device has
>>been saved already and the device is still in D0.  Setting that flag
>>will cause the next iterations of pci_pm_suspend_noirq() to set
>>state_saved for pci_pm_resume_noirq(), so that it always restores the
>>device state from the originally saved data, and avoid calling
>>pci_prepare_to_sleep() for the device.
>>
>>Fixes: 33e4f80ee69b ("ACPI / PM: Ignore spurious SCI wakeups from suspend-to-idle")
>>Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>Reviewed-by: Keith Busch <keith.busch@...el.com>
>>Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
>>Signed-off-by: Sasha Levin <sashal@...nel.org>
>>---
>>  drivers/pci/pci-driver.c | 17 ++++++++++++++++-
>>  include/linux/pci.h      |  1 +
>>  2 files changed, 17 insertions(+), 1 deletion(-)
>>
>>diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
>>index ea69b4dbab66..f5d66335fe53 100644
>>--- a/drivers/pci/pci-driver.c
>>+++ b/drivers/pci/pci-driver.c
>>@@ -726,6 +726,8 @@ static int pci_pm_suspend(struct device *dev)
>>  	struct pci_dev *pci_dev = to_pci_dev(dev);
>>  	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
>>+	pci_dev->skip_bus_pm = false;
>>+
>>  	if (pci_has_legacy_pm_support(pci_dev))
>>  		return pci_legacy_suspend(dev, PMSG_SUSPEND);
>>@@ -799,7 +801,20 @@ static int pci_pm_suspend_noirq(struct device *dev)
>>  		}
>>  	}
>>-	if (!pci_dev->state_saved) {
>>+	if (pci_dev->skip_bus_pm) {
>>+		/*
>>+		 * The function is running for the second time in a row without
>>+		 * going through full resume, which is possible only during
>>+		 * suspend-to-idle in a spurious wakeup case.  Moreover, the
>>+		 * device was originally left in D0, so its power state should
>>+		 * not be changed here and the device register values saved
>>+		 * originally should be restored on resume again.
>>+		 */
>>+		pci_dev->state_saved = true;
>>+	} else if (pci_dev->state_saved) {
>>+		if (pci_dev->current_state == PCI_D0)
>>+			pci_dev->skip_bus_pm = true;
>>+	} else {
>>  		pci_save_state(pci_dev);
>>  		if (pci_power_manageable(pci_dev))
>>  			pci_prepare_to_sleep(pci_dev);
>>diff --git a/include/linux/pci.h b/include/linux/pci.h
>>index 59f4d10568c6..430f3c335446 100644
>>--- a/include/linux/pci.h
>>+++ b/include/linux/pci.h
>>@@ -346,6 +346,7 @@ struct pci_dev {
>>  						   D3cold, not set for devices
>>  						   powered on/off by the
>>  						   corresponding bridge */
>>+	unsigned int	skip_bus_pm:1;	/* Internal: Skip bus-level PM */
>>  	unsigned int	ignore_hotplug:1;	/* Ignore hotplug events */
>>  	unsigned int	hotplug_user_indicators:1; /* SlotCtl indicators
>>  						      controlled exclusively by
>
>This has been reported to be problematic, I wouldn't recommend taking 
>it for -stable at this point.

I've dropped it, thank you.

--
Thanks,
Sasha