[RFC PATCH V2] virtio_pci: Add SR-IOV support

[Mark Rustad <mark.d.rustad@intel.com>]

Hardware-realized virtio-pci devices can implement SR-IOV, so this
patch enables its use. The device in question is an upcoming Intel
NIC that implements both a virtio-net PF and virtio-net VFs. These
are hardware realizations of what has been up to now been a software
interface.

The device in question has the following 4-part PCI IDs:

PF: device: 1af4 vendor: 1041 subvendor: 8086 subdevice: 15fe
VF: device: 1af4 vendor: 1041 subvendor: 8086 subdevice: 05fe

The patch needs no check for device ID, because the callback will
never be made for devices that do not assert the capability or
when run on a platform incapable of SR-IOV.

One reason for this patch is because the hardware requires the
vendor ID of a VF to be the same as the vendor ID of the PF that
created it. So it seemed logical to simply have a fully-functioning
virtio-net PF create the VFs. This patch makes that possible.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Reviewed-by: Alexander Duyck <alexander.h.duyck@intel.com>
---
Changes in V2:
- Simplified logic from previous version, removed added driver variable
- Disable SR-IOV on driver removal excapt when VFs are assigned
- Sent as RFC to virtio-dev, linux-pci, netdev, lkml and others
---
 drivers/virtio/virtio_pci_common.c |   47 ++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
index 48d4d1cf1cb6..78b53ffc4cee 100644
--- a/drivers/virtio/virtio_pci_common.c
+++ b/drivers/virtio/virtio_pci_common.c
@@ -572,6 +572,47 @@ static int virtio_pci_probe(struct pci_dev *pci_dev,
 	return rc;
 }
 
+#ifdef CONFIG_PCI_IOV
+static int virtio_pci_sriov_disable(struct pci_dev *pci_dev)
+{
+	/* If vfs are assigned we cannot shut down SR-IOV without causing
+	 * issues, so just leave the hardware available.
+	 */
+	if (pci_vfs_assigned(pci_dev)) {
+		dev_warn(&pci_dev->dev,
+			 "Unloading driver while VFs are assigned - VFs will not be deallocated\n");
+		return -EPERM;
+	}
+	pci_disable_sriov(pci_dev);
+	return 0;
+}
+
+static int virtio_pci_sriov_enable(struct pci_dev *pci_dev, int num_vfs)
+{
+	int rc = 0;
+
+	if (pci_num_vf(pci_dev))
+		return -EINVAL;
+
+	rc = pci_enable_sriov(pci_dev, num_vfs);
+	if (rc) {
+		dev_warn(&pci_dev->dev, "Failed to enable PCI sriov: %d\n", rc);
+		return rc;
+	}
+	dev_info(&pci_dev->dev, "SR-IOV enabled with %d VFs\n", num_vfs);
+	return num_vfs;
+}
+
+static int virtio_pci_sriov_configure(struct pci_dev *dev, int num_vfs)
+{
+	if (num_vfs)
+		return virtio_pci_sriov_enable(dev, num_vfs);
+	if (!pci_num_vf(dev))
+		return -EINVAL;
+	return virtio_pci_sriov_disable(dev);
+}
+#endif /* CONFIG_PCI_IOV */
+
 static void virtio_pci_remove(struct pci_dev *pci_dev)
 {
 	struct virtio_pci_device *vp_dev = pci_get_drvdata(pci_dev);
@@ -584,6 +625,9 @@ static void virtio_pci_remove(struct pci_dev *pci_dev)
 	else
 		virtio_pci_modern_remove(vp_dev);
 
+#ifdef CONFIG_PCI_IOV
+	virtio_pci_sriov_disable(pci_dev);
+#endif
 	pci_disable_device(pci_dev);
 	put_device(dev);
 }
@@ -596,6 +640,9 @@ static void virtio_pci_remove(struct pci_dev *pci_dev)
 #ifdef CONFIG_PM_SLEEP
 	.driver.pm	= &virtio_pci_pm_ops,
 #endif
+#ifdef CONFIG_PCI_IOV
+	.sriov_configure = virtio_pci_sriov_configure,
+#endif
 };
 
 module_pci_driver(virtio_pci_driver);