usb: gadget: hid: add configfs support

Make the hid function available for gadgets composed with configfs.

Signed-off-by: Andrzej Pietrasiewicz <[e-mail]>
Signed-off-by: Felipe Balbi <[e-mail]>

Documentation/ABI/testing/configfs-usb-gadget-hid

···
+What:		/config/usb-gadget/gadget/functions/hid.name
+Date:		Nov 2014
+KernelVersion:	3.19
+Description:
+		The attributes:
+
+		protocol	- HID protocol to use
+		report_desc	- blob corresponding to HID report descriptors
+				except the data passed through /dev/hidg<N>
+		report_length	- HID report length
+		subclass	- HID device subclass to use

Documentation/usb/gadget_hid.txt

···
 	You can add as many HID functions as you want, only limited by
 	the amount of interrupt endpoints your gadget driver supports.
 
+Configuration with configfs
+
+	Instead of adding fake platform devices and drivers in order to pass
+	some data to the kernel, if HID is a part of a gadget composed with
+	configfs the hidg_func_descriptor.report_desc is passed to the kernel
+	by writing the appropriate stream of bytes to a configfs attribute.
+
 Send and receive HID reports
 
 	HID reports can be sent/received using read/write on the

drivers/usb/gadget/Kconfig

···
 	  connections can then be made on the gadget system, using
 	  ALSA's aconnect utility etc.
 
+config USB_CONFIGFS_F_HID
+	boolean "HID function"
+	depends on USB_CONFIGFS
+	select USB_F_HID
+	help
+	  The HID function driver provides generic emulation of USB
+	  Human Interface Devices (HID).
+
+	  For more information, see Documentation/usb/gadget_hid.txt.
+
 source "drivers/usb/gadget/legacy/Kconfig"
 
 endchoice

drivers/usb/gadget/function/f_hid.c

···
 	return ret;
 }
 
+static inline struct f_hid_opts *to_f_hid_opts(struct config_item *item)
+{
+	return container_of(to_config_group(item), struct f_hid_opts,
+			    func_inst.group);
+}
+
+CONFIGFS_ATTR_STRUCT(f_hid_opts);
+CONFIGFS_ATTR_OPS(f_hid_opts);
+
+static void hid_attr_release(struct config_item *item)
+{
+	struct f_hid_opts *opts = to_f_hid_opts(item);
+
+	usb_put_function_instance(&opts->func_inst);
+}
+
+static struct configfs_item_operations hidg_item_ops = {
+	.release	= hid_attr_release,
+	.show_attribute	= f_hid_opts_attr_show,
+	.store_attribute = f_hid_opts_attr_store,
+};
+
+#define F_HID_OPT(name, prec, limit)					\
+static ssize_t f_hid_opts_##name##_show(struct f_hid_opts *opts, char *page)\
+{									\
+	int result;							\
+									\
+	mutex_lock(&opts->lock);					\
+	result = sprintf(page, "%d\n", opts->name);			\
+	mutex_unlock(&opts->lock);					\
+									\
+	return result;							\
+}									\
+									\
+static ssize_t f_hid_opts_##name##_store(struct f_hid_opts *opts,	\
+					 const char *page, size_t len)	\
+{									\
+	int ret;							\
+	u##prec num;							\
+									\
+	mutex_lock(&opts->lock);					\
+	if (opts->refcnt) {						\
+		ret = -EBUSY;						\
+		goto end;						\
+	}								\
+									\
+	ret = kstrtou##prec(page, 0, &num);				\
+	if (ret)							\
+		goto end;						\
+									\
+	if (num > limit) {						\
+		ret = -EINVAL;						\
+		goto end;						\
+	}								\
+	opts->name = num;						\
+	ret = len;							\
+									\
+end:									\
+	mutex_unlock(&opts->lock);					\
+	return ret;							\
+}									\
+									\
+static struct f_hid_opts_attribute f_hid_opts_##name =			\
+	__CONFIGFS_ATTR(name, S_IRUGO | S_IWUSR, f_hid_opts_##name##_show,\
+			f_hid_opts_##name##_store)
+
+F_HID_OPT(subclass, 8, 255);
+F_HID_OPT(protocol, 8, 255);
+F_HID_OPT(report_length, 16, 65536);
+
+static ssize_t f_hid_opts_report_desc_show(struct f_hid_opts *opts, char *page)
+{
+	int result;
+
+	mutex_lock(&opts->lock);
+	result = opts->report_desc_length;
+	memcpy(page, opts->report_desc, opts->report_desc_length);
+	mutex_unlock(&opts->lock);
+
+	return result;
+}
+
+static ssize_t f_hid_opts_report_desc_store(struct f_hid_opts *opts,
+					    const char *page, size_t len)
+{
+	int ret = -EBUSY;
+	char *d;
+
+	mutex_lock(&opts->lock);
+
+	if (opts->refcnt)
+		goto end;
+	if (len > PAGE_SIZE) {
+		ret = -ENOSPC;
+		goto end;
+	}
+	d = kmemdup(page, len, GFP_KERNEL);
+	if (!d) {
+		ret = -ENOMEM;
+		goto end;
+	}
+	kfree(opts->report_desc);
+	opts->report_desc = d;
+	opts->report_desc_length = len;
+	opts->report_desc_alloc = true;
+	ret = len;
+end:
+	mutex_unlock(&opts->lock);
+	return ret;
+}
+
+static struct f_hid_opts_attribute f_hid_opts_report_desc =
+	__CONFIGFS_ATTR(report_desc, S_IRUGO | S_IWUSR,
+			f_hid_opts_report_desc_show,
+			f_hid_opts_report_desc_store);
+
+static struct configfs_attribute *hid_attrs[] = {
+	&f_hid_opts_subclass.attr,
+	&f_hid_opts_protocol.attr,
+	&f_hid_opts_report_length.attr,
+	&f_hid_opts_report_desc.attr,
+	NULL,
+};
+
+static struct config_item_type hid_func_type = {
+	.ct_item_ops	= &hidg_item_ops,
+	.ct_attrs	= hid_attrs,
+	.ct_owner	= THIS_MODULE,
+};
+
 static inline void hidg_put_minor(int minor)
 {
 	ida_simple_remove(&hidg_ida, minor);
···
 	opts = kzalloc(sizeof(*opts), GFP_KERNEL);
 	if (!opts)
 		return ERR_PTR(-ENOMEM);
-
+	mutex_init(&opts->lock);
 	opts->func_inst.free_func_inst = hidg_free_inst;
 	ret = &opts->func_inst;
 
···
 		if (idr_is_empty(&hidg_ida.idr))
 			ghid_cleanup();
 	}
+	config_group_init_type_name(&opts->func_inst.group, "", &hid_func_type);
 
 unlock:
 	mutex_unlock(&hidg_ida_lock);
···
 static void hidg_free(struct usb_function *f)
 {
 	struct f_hidg *hidg;
+	struct f_hid_opts *opts;
 
 	hidg = func_to_hidg(f);
+	opts = container_of(f->fi, struct f_hid_opts, func_inst);
 	kfree(hidg->report_desc);
 	kfree(hidg);
+	mutex_lock(&opts->lock);
+	--opts->refcnt;
+	mutex_unlock(&opts->lock);
 }
 
 static void hidg_unbind(struct usb_configuration *c, struct usb_function *f)
···
 
 	opts = container_of(fi, struct f_hid_opts, func_inst);
 
+	mutex_lock(&opts->lock);
+	++opts->refcnt;
+
 	hidg->minor = opts->minor;
 	hidg->bInterfaceSubClass = opts->subclass;
 	hidg->bInterfaceProtocol = opts->protocol;
···
 					    GFP_KERNEL);
 		if (!hidg->report_desc) {
 			kfree(hidg);
+			mutex_unlock(&opts->lock);
 			return ERR_PTR(-ENOMEM);
 		}
 	}
+
+	mutex_unlock(&opts->lock);
 
 	hidg->func.name    = "hid";
 	hidg->func.bind    = hidg_bind;

drivers/usb/gadget/function/u_hid.h

···
 	unsigned short			report_desc_length;
 	unsigned char			*report_desc;
 	bool				report_desc_alloc;
+
+	/*
+	 * Protect the data form concurrent access by read/write
+	 * and create symlink/remove symlink.
+	 */
+	 struct mutex			lock;
+	 int				refcnt;
 };
 
 int ghid_setup(struct usb_gadget *g, int count);