[RFC PATCH 10/21] PCI: Add option to skip Bus Master Enable reset during kexec

[Vipin Sharma <vipinsh@google.com>]

Add bit field 'skip_kexec_clear_master' to struct pci_dev{}. Skip
clearing Bus Master Enable bit on PCI device during kexec reboot.

Devices preserved using live update might be performing a DMA
transaction during kexec. Skipping clearing this bit allows a device to
continue DMA while live update is in progress.

Signed-off-by: Vipin Sharma <vipinsh@google.com>
---
 drivers/pci/pci-driver.c | 6 ++++--
 include/linux/pci.h      | 2 ++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 302d61783f6c..6aab358dc27a 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -513,11 +513,13 @@ static void pci_device_shutdown(struct device *dev)
 	/*
 	 * 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.
+	 * devices in D3cold or unknown states. Don't clear the bit
+	 * if device has explicitly asked to skip it.
 	 * If it is not a kexec reboot, firmware will hit the PCI
 	 * devices with big hammer and stop their DMA any way.
 	 */
-	if (kexec_in_progress && (pci_dev->current_state <= PCI_D3hot))
+	if (kexec_in_progress && (pci_dev->current_state <= PCI_D3hot) &&
+	    !pci_dev->skip_kexec_clear_master)
 		pci_clear_master(pci_dev);
 }
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index d1fdf81fbe1e..8ce2d4528193 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -400,6 +400,8 @@ struct pci_dev {
 						   decoding during BAR sizing */
 	unsigned int	wakeup_prepared:1;
 	unsigned int	skip_bus_pm:1;	/* Internal: Skip bus-level PM */
+	unsigned int 	skip_kexec_clear_master:1; /* Don't clear the Bus Master
+						      Enable bit on kexec reboot */
 	unsigned int	ignore_hotplug:1;	/* Ignore hotplug events */
 	unsigned int	hotplug_user_indicators:1; /* SlotCtl indicators
 						      controlled exclusively by
-- 
2.51.0.858.gf9c4a03a3a-goog