[PATCH] PCI: Improve PCI config space writeback

At least one laptop blew up on resume from suspend with a black screen due
to a lack of this patch.  By only writing back config space that is
different, we minimise the possibility of accidents like this.

Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 13 insertions, 3 deletions

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 2329f941a0dc..d2520451f36b 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -461,9 +461,19 @@ int
 pci_restore_state(struct pci_dev *dev)
 {
         int i;
-
-        for (i = 0; i < 16; i++)
-                pci_write_config_dword(dev,i * 4, dev->saved_config_space[i]);
+        int val;
+
+        for (i = 0; i < 16; i++) {
+                pci_read_config_dword(dev, i * 4, &val);
+                if (val != dev->saved_config_space[i]) {
+                        printk(KERN_DEBUG "PM: Writing back config space on "
+                                "device %s at offset %x (was %x, writing %x)\n",
+                                pci_name(dev), i,
+                                val, (int)dev->saved_config_space[i]);
+                        pci_write_config_dword(dev,i * 4,
+                                dev->saved_config_space[i]);
+                }
+        }
         pci_restore_msi_state(dev);
         pci_restore_msix_state(dev);
         return 0;