commit dd414877b58b ("PCI/PM: Prevent runtime PM until claimed by a driver that supports it")
Author: Bjorn Helgaas [off-list ref]
Date:   Tue Nov 9 13:36:09 2021 -0600

    PCI/PM: Prevent runtime PM until claimed by a driver that supports it
    
    Previously we had a path that could call a driver's ->runtime_resume()
    method before calling the driver's ->probe() method, which is a problem
    because ->runtime_resume() often relies on initialization done in
    ->probe():
    
      local_pci_probe
        pm_runtime_get_sync
          ...
            pci_pm_runtime_resume
              if (!pci_dev->driver)
                return 0;                          <-- early exit
              dev->driver->pm->runtime_resume();   <-- driver ->runtime_resume()
        pci_dev->driver = pci_drv;
        pci_drv->probe()                           <-- driver ->probe()
    
    Prior to 2a4d9408c9e8 ("PCI: Use to_pci_driver() instead of
    pci_dev->driver"), we took the early exit, which avoided the problem.  But
    2a4d9408c9e8 removed pci_dev->driver (since it's redundant with
    device->driver), so we no longer take the early exit, which leads to havoc
    in ->runtime_resume().
    
    Similarly, we could call the driver's ->runtime_idle() method after its
    ->remove() method.
    
    Avoid the problem by dropping the pm_runtime_get_sync() and
    pm_runtime_put_sync() from local_pci_probe() and pci_device_remove(),
    respectively.
    
    Add pm_runtime_get_noresume(), which uses no driver PM callbacks, to the
    pci_pm_init() enumeration path.  This will prevent PM-runtime from touching
    the device until it has a driver that supports PM-runtime.
    
    Link: https://lore.kernel.org/r/CAJZ5v0impb8uscbp8LUTBMExfMoGz=cPrTWhSGh0GF_SANNKPQ@mail.gmail.com (local)
    Fixes: 2a4d9408c9e8 ("PCI: Use to_pci_driver() instead of pci_dev->driver")
    Reported-by: Robert Święcki [off-list ref]
    Suggested-by: Rafael J. Wysocki [off-list ref]
    Signed-off-by: Bjorn Helgaas [off-list ref]

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 1d98c974381c..41cdf510214f 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c

@@ -309,16 +309,6 @@ static long local_pci_probe(void *_ddi)
 	struct device *dev = &pci_dev->dev;
 	int rc;
 
-	/*
-	 * Unbound PCI devices are always put in D0, regardless of
-	 * runtime PM status.  During probe, the device is set to
-	 * active and the usage count is incremented.  If the driver
-	 * supports runtime PM, it should call pm_runtime_put_noidle(),
-	 * or any other runtime PM helper function decrementing the usage
-	 * count, in its probe routine and pm_runtime_get_noresume() in
-	 * its remove routine.
-	 */
-	pm_runtime_get_sync(dev);
 	rc = pci_drv->probe(pci_dev, ddi->id);
 	if (!rc)
 		return rc;

@@ -464,9 +454,6 @@ static void pci_device_remove(struct device *dev)
 	pcibios_free_irq(pci_dev);
 	pci_iov_remove(pci_dev);
 
-	/* Undo the runtime PM settings in local_pci_probe() */
-	pm_runtime_put_sync(dev);
-
 	/*
 	 * If the device is still on, set the power state as "unknown",
 	 * since it might change by the next time we load the driver.

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b88db815ee01..e9c38b994c73 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c

@@ -3097,7 +3097,15 @@ void pci_pm_init(struct pci_dev *dev)
 	u16 pmc;
 
 	pm_runtime_forbid(&dev->dev);
+
+	/*
+	 * Unbound PCI devices are always put in D0.  If the driver supports
+	 * runtime PM, it should call pm_runtime_put_noidle(), or any other
+	 * runtime PM helper function decrementing the usage count, in its
+	 * probe routine and pm_runtime_get_noresume() in its remove routine.
+	 */
 	pm_runtime_set_active(&dev->dev);
+	pm_runtime_get_noresume(&dev->dev);
 	pm_runtime_enable(&dev->dev);
 	device_enable_async_suspend(&dev->dev);
 	dev->wakeup_prepared = false;