PCI: Split out pci_dev lock/unlock and save/restore

Only cosmetic code changes to existing paths.  Expand the comment in
the new pci_dev_save_and_disable() function since there's a lot
hidden in that Command register write.
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>

drivers/pci/pci.c

@@ -3317,22 +3317,49 @@ static int __pci_dev_reset(struct pci_dev *dev, int probe)
 	return rc;
 }
 
+static void pci_dev_lock(struct pci_dev *dev)
+{
+	pci_cfg_access_lock(dev);
+	/* block PM suspend, driver probe, etc. */
+	device_lock(&dev->dev);
+}
+
+static void pci_dev_unlock(struct pci_dev *dev)
+{
+	device_unlock(&dev->dev);
+	pci_cfg_access_unlock(dev);
+}
+
+static void pci_dev_save_and_disable(struct pci_dev *dev)
+{
+	pci_save_state(dev);
+	/*
+	 * Disable the device by clearing the Command register, except for
+	 * INTx-disable which is set.  This not only disables MMIO and I/O port
+	 * BARs, but also prevents the device from being Bus Master, preventing
+	 * DMA from the device including MSI/MSI-X interrupts.  For PCI 2.3
+	 * compliant devices, INTx-disable prevents legacy interrupts.
+	 */
+	pci_write_config_word(dev, PCI_COMMAND, PCI_COMMAND_INTX_DISABLE);
+}
+
+static void pci_dev_restore(struct pci_dev *dev)
+{
+	pci_restore_state(dev);
+}
+
 static int pci_dev_reset(struct pci_dev *dev, int probe)
 {
 	int rc;
 
-	if (!probe) {
-		pci_cfg_access_lock(dev);
-		/* block PM suspend, driver probe, etc. */
-		device_lock(&dev->dev);
-	}
+	if (!probe)
+		pci_dev_lock(dev);
 
 	rc = __pci_dev_reset(dev, probe);
 
-	if (!probe) {
-		device_unlock(&dev->dev);
-		pci_cfg_access_unlock(dev);
-	}
+	if (!probe)
+		pci_dev_unlock(dev);
+
 	return rc;
 }
 /**
@@ -3423,17 +3450,11 @@ int pci_reset_function(struct pci_dev *dev)
 	if (rc)
 		return rc;
 
-	pci_save_state(dev);
-
-	/*
-	 * both INTx and MSI are disabled after the Interrupt Disable bit
-	 * is set and the Bus Master bit is cleared.
-	 */
-	pci_write_config_word(dev, PCI_COMMAND, PCI_COMMAND_INTX_DISABLE);
+	pci_dev_save_and_disable(dev);
 
 	rc = pci_dev_reset(dev, 0);
 
-	pci_restore_state(dev);
+	pci_dev_restore(dev);
 
 	return rc;
 }