PCI: endpoint: Allow user to create sub-directory of 'EPF Device' directory

Documentation/PCI/endpoint/pci-endpoint-cfs.rst explains how a user has to
create a directory in-order to create a 'EPF Device' that can be
configured/probed by 'EPF Driver'.

Allow user to create a sub-directory of 'EPF Device' directory for any
function specific attributes that has to be exposed to the user.

Link: https://lore.kernel.org/r/20210201195809.7342-11-kishon@ti.comSigned-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

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

@@ -490,7 +490,29 @@ static struct configfs_item_operations pci_epf_ops = {
 	.release		= pci_epf_release,
 };
 
+static struct config_group *pci_epf_type_make(struct config_group *group,
+					      const char *name)
+{
+	struct pci_epf_group *epf_group = to_pci_epf_group(&group->cg_item);
+	struct config_group *epf_type_group;
+
+	epf_type_group = pci_epf_type_add_cfs(epf_group->epf, group);
+	return epf_type_group;
+}
+
+static void pci_epf_type_drop(struct config_group *group,
+			      struct config_item *item)
+{
+	config_item_put(item);
+}
+
+static struct configfs_group_operations pci_epf_type_group_ops = {
+	.make_group     = &pci_epf_type_make,
+	.drop_item      = &pci_epf_type_drop,
+};
+
 static const struct config_item_type pci_epf_type = {
+	.ct_group_ops	= &pci_epf_type_group_ops,
 	.ct_item_ops	= &pci_epf_ops,
 	.ct_attrs	= pci_epf_attrs,
 	.ct_owner	= THIS_MODULE,
@@ -553,6 +575,7 @@ static struct config_group *pci_epf_make(struct config_group *group,
 		goto free_name;
 	}
 
+	epf->group = &epf_group->group;
 	epf_group->epf = epf;
 
 	kfree(epf_name);

include/linux/pci-epf.h

@@ -9,6 +9,7 @@
 #ifndef __LINUX_PCI_EPF_H
 #define __LINUX_PCI_EPF_H
 
+#include <linux/configfs.h>
 #include <linux/device.h>
 #include <linux/mod_devicetable.h>
 #include <linux/pci.h>
@@ -128,6 +129,7 @@ struct pci_epf_bar {
  *   EPC device
  * @sec_epc_bar: represents the BAR of EPF device associated with secondary EPC
  * @sec_epc_func_no: unique (physical) function number within the secondary EPC
+ * @group: configfs group associated with the EPF device
  */
 struct pci_epf {
 	struct device		dev;
@@ -150,6 +152,7 @@ struct pci_epf {
 	struct list_head	sec_epc_list;
 	struct pci_epf_bar	sec_epc_bar[6];
 	u8			sec_epc_func_no;
+	struct config_group	*group;
 };
 
 /**