Re: [PATCH] PCI: PM: Avoid possible suspend-to-idle issue

From: Kai-Heng Feng
Date: Tue Jun 11 2019 - 04:44:19 EST

Hi Rafael,

at 19:02, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:

On Friday, May 17, 2019 11:08:50 AM CEST Rafael J. Wysocki wrote:
From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

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@xxxxxxxxx>

I just found out this patch has a chance to freeze or reboot the system during suspend cycles.
What information do you need to debug?


drivers/pci/pci-driver.c | 17 ++++++++++++++++-
include/linux/pci.h | 1 +
2 files changed, 17 insertions(+), 1 deletion(-)

Index: linux-pm/drivers/pci/pci-driver.c
--- linux-pm.orig/drivers/pci/pci-driver.c
+++ linux-pm/drivers/pci/pci-driver.c
@@ -734,6 +734,8 @@ static int pci_pm_suspend(struct device
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);

@@ -827,7 +829,20 @@ static int pci_pm_suspend_noirq(struct d

- 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 {
if (pci_power_manageable(pci_dev))
Index: linux-pm/include/linux/pci.h
--- linux-pm.orig/include/linux/pci.h
+++ linux-pm/include/linux/pci.h
@@ -344,6 +344,7 @@ 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

Bjorn, I've assumed no concerns or objections from you regarding this one and
queued it up.

If that assumption is incorrect, please let me know.