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Subject[PATCH v2] PCI: PM: Skip devices in D0 for suspend-to-idle
Date
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Commit d491f2b75237 ("PCI: PM: Avoid possible suspend-to-idle issue")
attempted to avoid a problem with devices whose drivers want them to
stay in D0 over suspend-to-idle and resume, but it did not go as far
as it should with that.

Namely, first of all, the power state of a PCI bridge with a
downstream device in D0 must be D0 (based on the PCI PM spec r1.2,
sec 6, table 6-1, if the bridge is not in D0, there can be no PCI
transactions on its secondary bus), but that is not actively enforced
during system-wide PM transitions, so use the skip_bus_pm flag
introduced by commit d491f2b75237 for that.

Second, the configuration of devices left in D0 (whatever the reason)
during suspend-to-idle need not be changed and attempting to put them
into D0 again by force is pointless, so explicitly avoid doing that.

Fixes: d491f2b75237 ("PCI: PM: Avoid possible suspend-to-idle issue")
Reported-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Tested-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
---
drivers/pci/pci-driver.c | 47 +++++++++++++++++++++++++++++++++++------------
1 file changed, 35 insertions(+), 12 deletions(-)

Index: linux-pm/drivers/pci/pci-driver.c
===================================================================
--- linux-pm.orig/drivers/pci/pci-driver.c
+++ linux-pm/drivers/pci/pci-driver.c
@@ -524,7 +524,6 @@ static void pci_pm_default_resume_early(
pci_power_up(pci_dev);
pci_restore_state(pci_dev);
pci_pme_restore(pci_dev);
- pci_fixup_device(pci_fixup_resume_early, pci_dev);
}

/*
@@ -842,18 +841,16 @@ static int pci_pm_suspend_noirq(struct d

if (pci_dev->skip_bus_pm) {
/*
- * The function is running for the second time in a row without
+ * Either the device is a bridge with a child in D0 below it, or
+ * 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.
+ * suspend-to-idle in a spurious wakeup case. The device should
+ * be in D0 at this point, but if it is a bridge, it may be
+ * necessary to save its state.
*/
- 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_dev->state_saved)
+ pci_save_state(pci_dev);
+ } else if (!pci_dev->state_saved) {
pci_save_state(pci_dev);
if (pci_power_manageable(pci_dev))
pci_prepare_to_sleep(pci_dev);
@@ -862,6 +859,22 @@ static int pci_pm_suspend_noirq(struct d
dev_dbg(dev, "PCI PM: Suspend power state: %s\n",
pci_power_name(pci_dev->current_state));

+ if (pci_dev->current_state == PCI_D0) {
+ pci_dev->skip_bus_pm = true;
+ /*
+ * Per PCI PM r1.2, table 6-1, a bridge must be in D0 if any
+ * downstream device is in D0, so avoid changing the power state
+ * of the parent bridge by setting the skip_bus_pm flag for it.
+ */
+ if (pci_dev->bus->self)
+ pci_dev->bus->self->skip_bus_pm = true;
+ }
+
+ if (pci_dev->skip_bus_pm && !pm_suspend_via_firmware()) {
+ dev_dbg(dev, "PCI PM: Skipped\n");
+ goto Fixup;
+ }
+
pci_pm_set_unknown_state(pci_dev);

/*
@@ -909,7 +922,16 @@ static int pci_pm_resume_noirq(struct de
if (dev_pm_smart_suspend_and_suspended(dev))
pm_runtime_set_active(dev);

- pci_pm_default_resume_early(pci_dev);
+ /*
+ * In the suspend-to-idle case, devices left in D0 during suspend will
+ * stay in D0, so it is not necessary to restore or update their
+ * configuration here and attempting to put them into D0 again may
+ * confuse some firmware, so avoid doing that.
+ */
+ if (!pci_dev->skip_bus_pm || pm_suspend_via_firmware())
+ pci_pm_default_resume_early(pci_dev);
+
+ pci_fixup_device(pci_fixup_resume_early, pci_dev);

if (pci_has_legacy_pm_support(pci_dev))
return pci_legacy_resume_early(dev);
@@ -1200,6 +1222,7 @@ static int pci_pm_restore_noirq(struct d
}

pci_pm_default_resume_early(pci_dev);
+ pci_fixup_device(pci_fixup_resume_early, pci_dev);

if (pci_has_legacy_pm_support(pci_dev))
return pci_legacy_resume_early(dev);


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