usb: gadget: uvc: configfs: Add bFrameIndex attributes

- Add bFrameIndex as a UVCG_FRAME_ATTR_RO for each frame size.
- Automatically assign ascending bFrameIndex to each frame in a format.

Before all "bFrameindex" attributes were set to "1" with no way to
configure the gadget otherwise. This resulted in the host always
negotiating for bFrameIndex 1 (i.e. the first frame size of the gadget).
After the negotiation the host driver will set the user or application
selected frame size, while the gadget is actually set to the first frame
size.

Now, when the containing format is linked into the streaming header,
iterate over all child frame descriptors and assign ascending indices.
The automatically assigned indices can be read from the new read only
bFrameIndex configfs attribute in each frame descriptor item.

Signed-off-by: Joel Pepper <joel.pepper@rwth-aachen.de>
[Simplified documentation, renamed function, blank space update]
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

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

@@ -189,6 +189,10 @@ Date:		Dec 2014
 KernelVersion:	4.0
 Description:	Specific MJPEG frame descriptors
 
+		bFrameIndex		- unique id for this framedescriptor;
+					only defined after parent format is
+					linked into the streaming header;
+					read-only
 		dwFrameInterval		- indicates how frame interval can be
 					programmed; a number of values
 					separated by newline can be specified
@@ -240,6 +244,10 @@ Date:		Dec 2014
 KernelVersion:	4.0
 Description:	Specific uncompressed frame descriptors
 
+		bFrameIndex		- unique id for this framedescriptor;
+					only defined after parent format is
+					linked into the streaming header;
+					read-only
 		dwFrameInterval		- indicates how frame interval can be
 					programmed; a number of values
 					separated by newline can be specified

drivers/usb/gadget/function/uvc_configfs.c

@@ -868,6 +868,8 @@ static struct uvcg_streaming_header *to_uvcg_streaming_header(struct config_item
 	return container_of(item, struct uvcg_streaming_header, item);
 }
 
+static void uvcg_format_set_indices(struct config_group *fmt);
+
 static int uvcg_streaming_header_allow_link(struct config_item *src,
 					    struct config_item *target)
 {
@@ -915,6 +917,8 @@ static int uvcg_streaming_header_allow_link(struct config_item *src,
 	if (!target_fmt)
 		goto out;
 
+	uvcg_format_set_indices(to_config_group(target));
+
 	format_ptr = kzalloc(sizeof(*format_ptr), GFP_KERNEL);
 	if (!format_ptr) {
 		ret = -ENOMEM;
@@ -1146,6 +1150,41 @@ end:									\
 									\
 UVC_ATTR(uvcg_frame_, cname, aname);
 
+static ssize_t uvcg_frame_b_frame_index_show(struct config_item *item,
+					     char *page)
+{
+	struct uvcg_frame *f = to_uvcg_frame(item);
+	struct uvcg_format *fmt;
+	struct f_uvc_opts *opts;
+	struct config_item *opts_item;
+	struct config_item *fmt_item;
+	struct mutex *su_mutex = &f->item.ci_group->cg_subsys->su_mutex;
+	int result;
+
+	mutex_lock(su_mutex); /* for navigating configfs hierarchy */
+
+	fmt_item = f->item.ci_parent;
+	fmt = to_uvcg_format(fmt_item);
+
+	if (!fmt->linked) {
+		result = -EBUSY;
+		goto out;
+	}
+
+	opts_item = fmt_item->ci_parent->ci_parent->ci_parent;
+	opts = to_f_uvc_opts(opts_item);
+
+	mutex_lock(&opts->lock);
+	result = sprintf(page, "%d\n", f->frame.b_frame_index);
+	mutex_unlock(&opts->lock);
+
+out:
+	mutex_unlock(su_mutex);
+	return result;
+}
+
+UVC_ATTR_RO(uvcg_frame_, b_frame_index, bFrameIndex);
+
 #define noop_conversion(x) (x)
 
 UVCG_FRAME_ATTR(bm_capabilities, bmCapabilities, noop_conversion,
@@ -1294,6 +1333,7 @@ end:
 UVC_ATTR(uvcg_frame_, dw_frame_interval, dwFrameInterval);
 
 static struct configfs_attribute *uvcg_frame_attrs[] = {
+	&uvcg_frame_attr_b_frame_index,
 	&uvcg_frame_attr_bm_capabilities,
 	&uvcg_frame_attr_w_width,
 	&uvcg_frame_attr_w_height,
@@ -1373,6 +1413,22 @@ static void uvcg_frame_drop(struct config_group *group, struct config_item *item
 	config_item_put(item);
 }
 
+static void uvcg_format_set_indices(struct config_group *fmt)
+{
+	struct config_item *ci;
+	unsigned int i = 1;
+
+	list_for_each_entry(ci, &fmt->cg_children, ci_entry) {
+		struct uvcg_frame *frm;
+
+		if (ci->ci_type != &uvcg_frame_type)
+			continue;
+
+		frm = to_uvcg_frame(ci);
+		frm->frame.b_frame_index = i++;
+	}
+}
+
 /* -----------------------------------------------------------------------------
  * streaming/uncompressed/<NAME>
  */