PCI/PM: Keep runtime PM enabled for unbound PCI devices

For unbound PCI devices, what we need is:

 - Always in D0 state, because some devices do not work again after
   being put into D3 by the PCI bus.

 - In SUSPENDED state if allowed, so that the parent devices can still
   be put into low power state.

To satisfy these requirements, the runtime PM for the unbound PCI
devices are disabled and set to SUSPENDED state.  One issue of this
solution is that the PCI devices will be put into SUSPENDED state even
if the SUSPENDED state is forbidden via the sysfs interface
(.../power/control) of the device.  This is not an issue for most
devices, because most PCI devices are not used at all if unbound.
But there are exceptions.  For example, unbound VGA card can be used
for display, but suspending its parents makes it stop working.

To fix the issue, we keep the runtime PM enabled when the PCI devices
are unbound.  But the runtime PM callbacks will do nothing if the PCI
devices are unbound.  This way, we can put the PCI devices into
SUSPENDED state without putting the PCI devices into D3 state.

Reference: https://bugzilla.kernel.org/show_bug.cgi?id=48201
Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
CC: stable@vger.kernel.org          # v3.6+

drivers/pci/pci-driver.c

@@ -256,31 +256,26 @@ struct drv_dev_and_id {
 static long local_pci_probe(void *_ddi)
 {
 	struct drv_dev_and_id *ddi = _ddi;
-	struct device *dev = &ddi->dev->dev;
-	struct device *parent = dev->parent;
+	struct pci_dev *pci_dev = ddi->dev;
+	struct pci_driver *pci_drv = ddi->drv;
+	struct device *dev = &pci_dev->dev;
 	int rc;
 
-	/* The parent bridge must be in active state when probing */
-	if (parent)
-		pm_runtime_get_sync(parent);
-	/* Unbound PCI devices are always set to disabled and suspended.
-	 * During probe, the device is set to enabled and active and the
-	 * usage count is incremented.  If the driver supports runtime PM,
-	 * it should call pm_runtime_put_noidle() in its probe routine and
-	 * pm_runtime_get_noresume() in its remove routine.
+	/*
+	 * 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()
+	 * in its probe routine and pm_runtime_get_noresume() in its
+	 * remove routine.
 	 */
-	pm_runtime_get_noresume(dev);
-	pm_runtime_set_active(dev);
-	pm_runtime_enable(dev);
-
-	rc = ddi->drv->probe(ddi->dev, ddi->id);
+	pm_runtime_get_sync(dev);
+	pci_dev->driver = pci_drv;
+	rc = pci_drv->probe(pci_dev, ddi->id);
 	if (rc) {
-		pm_runtime_disable(dev);
-		pm_runtime_set_suspended(dev);
-		pm_runtime_put_noidle(dev);
+		pci_dev->driver = NULL;
+		pm_runtime_put_sync(dev);
 	}
-	if (parent)
-		pm_runtime_put(parent);
 	return rc;
 }
 
@@ -330,10 +325,8 @@ __pci_device_probe(struct pci_driver *drv, struct pci_dev *pci_dev)
 		id = pci_match_device(drv, pci_dev);
 		if (id)
 			error = pci_call_probe(drv, pci_dev, id);
-		if (error >= 0) {
-			pci_dev->driver = drv;
+		if (error >= 0)
 			error = 0;
-		}
 	}
 	return error;
 }
@@ -369,9 +362,7 @@ static int pci_device_remove(struct device * dev)
 	}
 
 	/* Undo the runtime PM settings in local_pci_probe() */
-	pm_runtime_disable(dev);
-	pm_runtime_set_suspended(dev);
-	pm_runtime_put_noidle(dev);
+	pm_runtime_put_sync(dev);
 
 	/*
 	 * If the device is still on, set the power state as "unknown",
@@ -994,6 +985,13 @@ static int pci_pm_runtime_suspend(struct device *dev)
 	pci_power_t prev = pci_dev->current_state;
 	int error;
 
+	/*
+	 * If pci_dev->driver is not set (unbound), the device should
+	 * always remain in D0 regardless of the runtime PM status
+	 */
+	if (!pci_dev->driver)
+		return 0;
+
 	if (!pm || !pm->runtime_suspend)
 		return -ENOSYS;
 
@@ -1029,6 +1027,13 @@ static int pci_pm_runtime_resume(struct device *dev)
 	struct pci_dev *pci_dev = to_pci_dev(dev);
 	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
 
+	/*
+	 * If pci_dev->driver is not set (unbound), the device should
+	 * always remain in D0 regardless of the runtime PM status
+	 */
+	if (!pci_dev->driver)
+		return 0;
+
 	if (!pm || !pm->runtime_resume)
 		return -ENOSYS;
 
@@ -1046,8 +1051,16 @@ static int pci_pm_runtime_resume(struct device *dev)
 
 static int pci_pm_runtime_idle(struct device *dev)
 {
+	struct pci_dev *pci_dev = to_pci_dev(dev);
 	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
 
+	/*
+	 * If pci_dev->driver is not set (unbound), the device should
+	 * always remain in D0 regardless of the runtime PM status
+	 */
+	if (!pci_dev->driver)
+		goto out;
+
 	if (!pm)
 		return -ENOSYS;
 
@@ -1057,8 +1070,8 @@ static int pci_pm_runtime_idle(struct device *dev)
 			return ret;
 	}
 
+out:
 	pm_runtime_suspend(dev);
-
 	return 0;
 }
 

drivers/pci/pci.c

@@ -1900,6 +1900,8 @@ void pci_pm_init(struct pci_dev *dev)
 	u16 pmc;
 
 	pm_runtime_forbid(&dev->dev);
+	pm_runtime_set_active(&dev->dev);
+	pm_runtime_enable(&dev->dev);
 	device_enable_async_suspend(&dev->dev);
 	dev->wakeup_prepared = false;