[PATCH 4/4] PCI: Avoid unnecessary resume on shutdown

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We currently perform a mandatory runtime resume of all PCI devices on
->shutdown.  However it is pointless to wake devices only to immediately
power them down afterwards.  (Or have the firmware reset them, in case
of a reboot.)

It seems there are only two cases when a runtime resume is actually
necessary:  If the driver has declared a ->shutdown callback or if kexec
is in progress.

Constrain resume of a device to these cases and let it slumber
otherwise, thereby conserving energy and speeding up shutdown.

Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
---
 drivers/pci/pci-driver.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index fd4b9c4..09a4e56 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -459,6 +459,11 @@ static void pci_device_shutdown(struct device *dev)
 	struct pci_dev *pci_dev = to_pci_dev(dev);
 	struct pci_driver *drv = pci_dev->driver;
 
+	/* Fast path for suspended devices */
+	if (pm_runtime_suspended(dev) && (!drv || !drv->shutdown) &&
+	    !kexec_in_progress)
+		return;
+
 	pm_runtime_resume(dev);
 
 	if (drv && drv->shutdown)
-- 
2.8.1

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