PCI: Add sysfs sriov_drivers_autoprobe to control VF driver binding

Sometimes it is not desirable to bind SR-IOV VFs to drivers.  This can save
host side resource usage by VF instances that will be assigned to VMs.

Add a new PCI sysfs interface "sriov_drivers_autoprobe" to control that
from the PF.  To modify it, echo 0/n/N (disable probe) or 1/y/Y (enable
probe) to:

  /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_drivers_autoprobe

Note that this must be done before enabling VFs.  The change will not take
effect if VFs are already enabled.  Simply, one can disable VFs by setting
sriov_numvfs to 0, choose whether to probe or not, and then re-enable the
VFs by restoring sriov_numvfs.

[bhelgaas: changelog, ABI doc]
Signed-off-by: Bodong Wang <bodong@mellanox.com>
Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>

2 files changed, 34 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index 5a1732b78707..b728f700340d 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci
+++ b/Documentation/ABI/testing/sysfs-bus-pci
@@ -301,3 +301,25 @@ Contact:	Emil Velikov <emil.l.velikov@gmail.com>
 Description:
 		This file contains the revision field of the the PCI device.
 		The value comes from device config space. The file is read only.
+
+What:		/sys/bus/pci/devices/.../sriov_drivers_autoprobe
+Date:		April 2017
+Contact:	Bodong Wang<bodong@mellanox.com>
+Description:
+		This file is associated with the PF of a device that
+		supports SR-IOV.  It determines whether newly-enabled VFs
+		are immediately bound to a driver.  It initially contains
+		1, which means the kernel automatically binds VFs to a
+		compatible driver immediately after they are enabled.  If
+		an application writes 0 to the file before enabling VFs,
+		the kernel will not bind VFs to a driver.
+
+		A typical use case is to write 0 to this file, then enable
+		VFs, then assign the newly-created VFs to virtual machines.
+		Note that changing this file does not affect already-
+		enabled VFs.  In this scenario, the user must first disable
+		the VFs, write 0 to sriov_drivers_autoprobe, then re-enable
+		the VFs.
+
+		This is similar to /sys/bus/pci/drivers_autoprobe, but
+		affects only the VFs associated with a specific PF.
diff --git a/Documentation/PCI/pci-iov-howto.txt b/Documentation/PCI/pci-iov-howto.txt
index 2d91ae251982..d2a84151e99c 100644
--- a/Documentation/PCI/pci-iov-howto.txt
+++ b/Documentation/PCI/pci-iov-howto.txt
@@ -68,6 +68,18 @@ To disable SR-IOV capability:
 	echo  0 > \
         /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_numvfs
 
+To enable auto probing VFs by a compatible driver on the host, run
+command below before enabling SR-IOV capabilities. This is the
+default behavior.
+	echo 1 > \
+        /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_drivers_autoprobe
+
+To disable auto probing VFs by a compatible driver on the host, run
+command below before enabling SR-IOV capabilities. Updating this
+entry will not affect VFs which are already probed.
+	echo  0 > \
+        /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_drivers_autoprobe
+
 3.2 Usage example
 
 Following piece of code illustrates the usage of the SR-IOV API.