PCI: endpoint: Add support to link a physical function to a virtual function

While the physical function has to be linked to endpoint controller, the
virtual function has to be linked to a physical function. Add support to
link a physical function to a virtual function in pci-ep-cfs.

Link: https://lore.kernel.org/r/20210819123343.1951-4-kishon@ti.comSigned-off-by: NKishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>

drivers/pci/endpoint/pci-ep-cfs.c

@@ -475,6 +475,28 @@ static struct configfs_attribute *pci_epf_attrs[] = {
 	NULL,
 };
 
+static int pci_epf_vepf_link(struct config_item *epf_pf_item,
+			     struct config_item *epf_vf_item)
+{
+	struct pci_epf_group *epf_vf_group = to_pci_epf_group(epf_vf_item);
+	struct pci_epf_group *epf_pf_group = to_pci_epf_group(epf_pf_item);
+	struct pci_epf *epf_pf = epf_pf_group->epf;
+	struct pci_epf *epf_vf = epf_vf_group->epf;
+
+	return pci_epf_add_vepf(epf_pf, epf_vf);
+}
+
+static void pci_epf_vepf_unlink(struct config_item *epf_pf_item,
+				struct config_item *epf_vf_item)
+{
+	struct pci_epf_group *epf_vf_group = to_pci_epf_group(epf_vf_item);
+	struct pci_epf_group *epf_pf_group = to_pci_epf_group(epf_pf_item);
+	struct pci_epf *epf_pf = epf_pf_group->epf;
+	struct pci_epf *epf_vf = epf_vf_group->epf;
+
+	pci_epf_remove_vepf(epf_pf, epf_vf);
+}
+
 static void pci_epf_release(struct config_item *item)
 {
 	struct pci_epf_group *epf_group = to_pci_epf_group(item);
@@ -487,6 +509,8 @@ static void pci_epf_release(struct config_item *item)
 }
 
 static struct configfs_item_operations pci_epf_ops = {
+	.allow_link		= pci_epf_vepf_link,
+	.drop_link		= pci_epf_vepf_unlink,
 	.release		= pci_epf_release,
 };