[PATCH] PCI / PM: Don't runtime suspend when device only supports wakeup from D0

[Kai-Heng Feng <kai.heng.feng@canonical.com>]

There's an xHC device that doesn't wake when a USB device gets plugged
to its USB port. The driver's own runtime suspend callback was called,
PME signaling was enabled, but it stays at PCI D0.

A PCI device can be runtime suspended to D0 when it supports D0 PME and
its _S0W reports D0. Theoratically this should work, but as [1]
specifies, D0 doesn't have wakeup capability.

To avoid this problematic situation, we should avoid runtime suspend if
D0 is the only state that can wake up the device.

[1] https://docs.microsoft.com/en-us/windows-hardware/drivers/kernel/device-working-state-d0

Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
---
 drivers/pci/pci-driver.c | 5 +++++
 drivers/pci/pci.c        | 2 +-
 include/linux/pci.h      | 3 +++
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index cae630fe6387..15a6310c5d7b 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -1251,6 +1251,11 @@ static int pci_pm_runtime_suspend(struct device *dev)
 		return 0;
 	}
 
+	if (pci_target_state(pci_dev, device_can_wakeup(dev)) == PCI_D0) {
+		dev_dbg(dev, "D0 doesn't have wakeup capability\n");
+		return -EBUSY;
+	}
+
 	pci_dev->state_saved = false;
 	if (pm && pm->runtime_suspend) {
 		error = pm->runtime_suspend(dev);
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 8abc843b1615..ceee6efbbcfe 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -2294,7 +2294,7 @@ EXPORT_SYMBOL(pci_wake_from_d3);
  * If the platform can't manage @dev, return the deepest state from which it
  * can generate wake events, based on any available PME info.
  */
-static pci_power_t pci_target_state(struct pci_dev *dev, bool wakeup)
+pci_power_t pci_target_state(struct pci_dev *dev, bool wakeup)
 {
 	pci_power_t target_state = PCI_D3hot;
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 4a5a84d7bdd4..91e8dc4d04aa 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1188,6 +1188,7 @@ bool pci_pme_capable(struct pci_dev *dev, pci_power_t state);
 void pci_pme_active(struct pci_dev *dev, bool enable);
 int pci_enable_wake(struct pci_dev *dev, pci_power_t state, bool enable);
 int pci_wake_from_d3(struct pci_dev *dev, bool enable);
+pci_power_t pci_target_state(struct pci_dev *dev, bool wakeup);
 int pci_prepare_to_sleep(struct pci_dev *dev);
 int pci_back_from_sleep(struct pci_dev *dev);
 bool pci_dev_run_wake(struct pci_dev *dev);
@@ -1672,6 +1673,8 @@ static inline int pci_set_power_state(struct pci_dev *dev, pci_power_t state)
 { return 0; }
 static inline int pci_wake_from_d3(struct pci_dev *dev, bool enable)
 { return 0; }
+pci_power_t pci_target_state(struct pci_dev *dev, bool wakeup)
+{ return PCI_D0; }
 static inline pci_power_t pci_choose_state(struct pci_dev *dev,
 					   pm_message_t state)
 { return PCI_D0; }
-- 
2.17.1