On Wed, Sep 14, 2016 at 02:29:52AM +0200, Rafael J. Wysocki wrote:

On Wednesday, August 31, 2016 08:15:18 AM Lukas Wunner wrote:

quoted

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 <redacted>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
---
 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)

What happens if runtime suspend or resume of the device happens here?

You're right, good point.  How about disabling runtime PM then, like this:

	/* Fast path for suspended devices */
	if (pm_runtime_status_suspended(dev) && (!drv || !drv->shutdown) &&
	    !kexec_in_progress) {
		pm_runtime_disable(dev);
		if (pm_runtime_status_suspended(dev))
			return;
		pm_runtime_enable(dev);
	}

All dependents (children, and in the future, consumers) should already
have been treated at that point, due to the ordering of devices_kset->list.

Thanks!

Lukas