PCI/MSI: Add "msi_bus" sysfs MSI/MSI-X control for endpoints

The "msi_bus" sysfs file for bridges sets a bus flag to allow or disallow
future driver requests for MSI or MSI-X.  Previously, the sysfs file
existed for endpoints but did nothing.

Add "msi_bus" support for endpoints, so an administrator can prevent the
use of MSI and MSI-X for individual devices.

Note that as for bridges, these changes only affect future driver requests
for MSI or MSI-X, so drivers may need to be reloaded.

Add documentation for the "msi_bus" sysfs file.

[bhelgaas: changelog, comments, add "subordinate", add endpoint printk,
rework bus_flags setting, make bus_flags printk unconditional]
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index 6615fda0abfb..ee6c04036492 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci
+++ b/Documentation/ABI/testing/sysfs-bus-pci
@@ -65,6 +65,16 @@ Description:
                 force a rescan of all PCI buses in the system, and
                 re-discover previously removed devices.
 
+What:           /sys/bus/pci/devices/.../msi_bus
+Date:           September 2014
+Contact:        Linux PCI developers <linux-pci@vger.kernel.org>
+Description:
+                Writing a zero value to this attribute disallows MSI and
+                MSI-X for any future drivers of the device.  If the device
+                is a bridge, MSI and MSI-X will be disallowed for future
+                drivers of all child devices under the bridge.  Drivers
+                must be reloaded for the new setting to take effect.
+
 What:           /sys/bus/pci/devices/.../msi_irqs/
 Date:           September, 2011
 Contact:        Neil Horman <nhorman@tuxdriver.com>