PCI: SRIOV control and status via sysfs (documentation)

Add documentation of new sysfs files and new pci_driver SRIOV
configuration interface.

[bhelgaas: changelog]
Signed-off: Donald Dutile <ddutile@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

Documentation/ABI/testing/sysfs-bus-pci

@@ -222,3 +222,37 @@ Description:
 		satisfied too.  Reading this attribute will show the current
 		value of d3cold_allowed bit.  Writing this attribute will set
 		the value of d3cold_allowed bit.
+
+What:		/sys/bus/pci/devices/.../sriov_totalvfs
+Date:		November 2012
+Contact:	Donald Dutile <ddutile@redhat.com>
+Description:
+		This file appears when a physical PCIe device supports SR-IOV.
+		Userspace applications can read this file to determine the
+		maximum number of Virtual Functions (VFs) a PCIe physical
+		function (PF) can support. Typically, this is the value reported
+		in the PF's SR-IOV extended capability structure's TotalVFs
+		element.  Drivers have the ability at probe time to reduce the
+		value read from this file via the pci_sriov_set_totalvfs()
+		function.
+
+What:		/sys/bus/pci/devices/.../sriov_numvfs
+Date:		November 2012
+Contact:	Donald Dutile <ddutile@redhat.com>
+Description:
+		This file appears when a physical PCIe device supports SR-IOV.
+		Userspace applications can read and write to this file to
+		determine and control the enablement or disablement of Virtual
+		Functions (VFs) on the physical function (PF). A read of this
+		file will return the number of VFs that are enabled on this PF.
+		A number written to this file will enable the specified
+		number of VFs. A userspace application would typically read the
+		file and check that the value is zero, and then write the number
+		of VFs that should be enabled on the PF; the value written
+		should be less than or equal to the value in the sriov_totalvfs
+		file. A userspace application wanting to disable the VFs would
+		write a zero to this file. The core ensures that valid values
+		are written to this file, and returns errors when values are not
+		valid.  For example, writing a 2 to this file when sriov_numvfs
+		is not 0 and not 2 already will return an error. Writing a 10
+		when the value of sriov_totalvfs is 8 will return an error.

Documentation/PCI/pci-iov-howto.txt

@@ -2,6 +2,9 @@
 		Copyright (C) 2009 Intel Corporation
 		    Yu Zhao <yu.zhao@intel.com>
 
+		Update: November 2012
+			-- sysfs-based SRIOV enable-/disable-ment
+		Donald Dutile <ddutile@redhat.com>
 
 1. Overview
 
@@ -24,10 +27,21 @@ real existing PCI device.
 
 2.1 How can I enable SR-IOV capability
 
-The device driver (PF driver) will control the enabling and disabling
-of the capability via API provided by SR-IOV core. If the hardware
-has SR-IOV capability, loading its PF driver would enable it and all
-VFs associated with the PF.
+Multiple methods are available for SR-IOV enablement.
+In the first method, the device driver (PF driver) will control the
+enabling and disabling of the capability via API provided by SR-IOV core.
+If the hardware has SR-IOV capability, loading its PF driver would
+enable it and all VFs associated with the PF.  Some PF drivers require
+a module parameter to be set to determine the number of VFs to enable.
+In the second method, a write to the sysfs file sriov_numvfs will
+enable and disable the VFs associated with a PCIe PF.  This method
+enables per-PF, VF enable/disable values versus the first method,
+which applies to all PFs of the same device.  Additionally, the
+PCI SRIOV core support ensures that enable/disable operations are
+valid to reduce duplication in multiple drivers for the same
+checks, e.g., check numvfs == 0 if enabling VFs, ensure
+numvfs <= totalvfs.
+The second method is the recommended method for new/future VF devices.
 
 2.2 How can I use the Virtual Functions
 
@@ -40,13 +54,22 @@ requires device driver that is same as a normal PCI device's.
 3.1 SR-IOV API
 
 To enable SR-IOV capability:
+(a) For the first method, in the driver:
 	int pci_enable_sriov(struct pci_dev *dev, int nr_virtfn);
 	'nr_virtfn' is number of VFs to be enabled.
+(b) For the second method, from sysfs:
+	echo 'nr_virtfn' > \
+        /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_numvfs
 
 To disable SR-IOV capability:
+(a) For the first method, in the driver:
 	void pci_disable_sriov(struct pci_dev *dev);
+(b) For the second method, from sysfs:
+	echo  0 > \
+        /sys/bus/pci/devices/<DOMAIN:BUS:DEVICE.FUNCTION>/sriov_numvfs
 
 To notify SR-IOV core of Virtual Function Migration:
+(a) In the driver:
 	irqreturn_t pci_sriov_migration(struct pci_dev *dev);
 
 3.2 Usage example
@@ -88,6 +111,22 @@ static void dev_shutdown(struct pci_dev *dev)
 	...
 }
 
+static int dev_sriov_configure(struct pci_dev *dev, int numvfs)
+{
+	if (numvfs > 0) {
+		...
+		pci_enable_sriov(dev, numvfs);
+		...
+		return numvfs;
+	}
+	if (numvfs == 0) {
+		....
+		pci_disable_sriov(dev);
+		...
+		return 0;
+	}
+}
+
 static struct pci_driver dev_driver = {
 	.name =		"SR-IOV Physical Function driver",
 	.id_table =	dev_id_table,
@@ -96,4 +135,5 @@ static struct pci_driver dev_driver = {
 	.suspend =	dev_suspend,
 	.resume =	dev_resume,
 	.shutdown =	dev_shutdown,
+	.sriov_configure = dev_sriov_configure,
 };