PCI: Disable Bus Master only on kexec reboot

Add a flag to tell the PCI subsystem that kernel is shutting down in
preparation to kexec a kernel.  Add code in PCI subsystem to use this flag
to clear Bus Master bit on PCI devices only in case of kexec reboot.

This fixes a power-off problem on Acer Aspire V5-573G and likely other
machines and avoids any other issues caused by clearing Bus Master bit on
PCI devices in normal shutdown path.  The problem was introduced by
b566a22c2332 ("PCI: disable Bus Master on PCI device shutdown").

This patch is based on discussion at
http://marc.info/?l=linux-pci&m=138425645204355&w=2

Link: https://bugzilla.kernel.org/show_bug.cgi?id=63861
Reported-by: Chang Liu <cl91tp@gmail.com>
Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: stable@vger.kernel.org	# v3.5+

1 files changed, 9 insertions, 3 deletions

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 7edd5c307446..25f0bc659164 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -19,6 +19,7 @@
 #include <linux/cpu.h>
 #include <linux/pm_runtime.h>
 #include <linux/suspend.h>
+#include <linux/kexec.h>
 #include "pci.h"
 
 struct pci_dynid {
@@ -415,12 +416,17 @@ static void pci_device_shutdown(struct device *dev)
         pci_msi_shutdown(pci_dev);
         pci_msix_shutdown(pci_dev);
 
+#ifdef CONFIG_KEXEC
         /*
-         * Turn off Bus Master bit on the device to tell it to not
-         * continue to do DMA. Don't touch devices in D3cold or unknown states.
+         * If this is a kexec reboot, turn off Bus Master bit on the
+         * device to tell it to not continue to do DMA. Don't touch
+         * devices in D3cold or unknown states.
+         * If it is not a kexec reboot, firmware will hit the PCI
+         * devices with big hammer and stop their DMA any way.
          */
-        if (pci_dev->current_state <= PCI_D3hot)
+        if (kexec_in_progress && (pci_dev->current_state <= PCI_D3hot))
                 pci_clear_master(pci_dev);
+#endif
 }
 
 #ifdef CONFIG_PM