usb: gadget: uvc: Add new enable_interrupt_ep attribute

Add a new attribute to the default control config group that allows
users to specify whether they want to enable the optional interrupt
endpoint for the VideoControl interface.
Signed-off-by: Daniel Scally <dan.scally@ideasonboard.com>
Link: https://lore.kernel.org/r/20230130105045.120886-3-dan.scally@ideasonboard.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -15,11 +15,13 @@ Date:		Dec 2014
 KernelVersion:	4.0
 Description:	Control descriptors
 
-		All attributes read only:
+		All attributes read only except enable_interrupt_ep:
 
 		================	=============================
 		bInterfaceNumber	USB interface number for this
 					streaming interface
+		enable_interrupt_ep	flag to enable the interrupt
+					endpoint for the VC interface
 		================	=============================
 
 What:		/config/usb-gadget/gadget/functions/uvc.name/control/class

drivers/usb/gadget/function/u_uvc.h

@@ -29,6 +29,8 @@ struct f_uvc_opts {
 	unsigned int					streaming_interface;
 	char						function_name[32];
 
+	bool						enable_interrupt_ep;
+
 	/*
 	 * Control descriptors array pointers for full-/high-speed and
 	 * super-speed. They point by default to the uvc_fs_control_cls and

drivers/usb/gadget/function/uvc_configfs.c

@@ -716,8 +716,61 @@ static ssize_t uvcg_default_control_b_interface_number_show(
 
 UVC_ATTR_RO(uvcg_default_control_, b_interface_number, bInterfaceNumber);
 
+static ssize_t uvcg_default_control_enable_interrupt_ep_show(
+	struct config_item *item, char *page)
+{
+	struct config_group *group = to_config_group(item);
+	struct mutex *su_mutex = &group->cg_subsys->su_mutex;
+	struct config_item *opts_item;
+	struct f_uvc_opts *opts;
+	int result = 0;
+
+	mutex_lock(su_mutex); /* for navigating configfs hierarchy */
+
+	opts_item = item->ci_parent;
+	opts = to_f_uvc_opts(opts_item);
+
+	mutex_lock(&opts->lock);
+	result += sprintf(page, "%u\n", opts->enable_interrupt_ep);
+	mutex_unlock(&opts->lock);
+
+	mutex_unlock(su_mutex);
+
+	return result;
+}
+
+static ssize_t uvcg_default_control_enable_interrupt_ep_store(
+	struct config_item *item, const char *page, size_t len)
+{
+	struct config_group *group = to_config_group(item);
+	struct mutex *su_mutex = &group->cg_subsys->su_mutex;
+	struct config_item *opts_item;
+	struct f_uvc_opts *opts;
+	ssize_t ret;
+	u8 num;
+
+	ret = kstrtou8(page, 0, &num);
+	if (ret)
+		return ret;
+
+	mutex_lock(su_mutex); /* for navigating configfs hierarchy */
+
+	opts_item = item->ci_parent;
+	opts = to_f_uvc_opts(opts_item);
+
+	mutex_lock(&opts->lock);
+	opts->enable_interrupt_ep = num;
+	mutex_unlock(&opts->lock);
+
+	mutex_unlock(su_mutex);
+
+	return len;
+}
+UVC_ATTR(uvcg_default_control_, enable_interrupt_ep, enable_interrupt_ep);
+
 static struct configfs_attribute *uvcg_default_control_attrs[] = {
 	&uvcg_default_control_attr_b_interface_number,
+	&uvcg_default_control_attr_enable_interrupt_ep,
 	NULL,
 };