usb: gadget: uvc: fix multiple opens

Currently, the UVC function is activated when open on the corresponding
v4l2 device is called.  On another open the activation of the function
fails since the deactivation counter in `usb_function_activate` equals
0. However the error is not returned to userspace since the open of the
v4l2 device is successful.

On a close the function is deactivated (since deactivation counter still
equals 0) and the video is disabled in `uvc_v4l2_release`, although the
UVC application potentially is streaming.

Move activation of UVC function to subscription on UVC_EVENT_SETUP
because there we can guarantee for a userspace application utilizing
UVC.  Block subscription on UVC_EVENT_SETUP while another application
already is subscribed to it, indicated by `bool func_connected` in
`struct uvc_device`.  Extend the `struct uvc_file_handle` with member
`bool is_uvc_app_handle` to tag it as the handle used by the userspace
UVC application.

With this a process is able to check capabilities of the v4l2 device
without deactivating the function for the actual UVC application.

Reviewed-By: Michael Tretter <m.tretter@pengutronix.de>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Thomas Haemmerle <thomas.haemmerle@wolfvision.net>
Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Acked-by: Felipe Balbi <balbi@kernel.org>
Link: https://lore.kernel.org/r/20211003201355.24081-1-m.grzeschik@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
index 255a61bd6a6a8d58d552b0d32b9bba7b01d11489..9d5f17b551bbd1a7ffd61b46108e4fdc24e0ea42 100644 (file)
--- a/drivers/usb/gadget/function/uvc.h
+++ b/drivers/usb/gadget/function/uvc.h
@@ -126,6 +126,7 @@ struct uvc_device {
        enum uvc_state state;
        struct usb_function func;
        struct uvc_video video;
+       bool func_connected;
 
        /* Descriptors */
        struct {
@@ -156,6 +157,7 @@ static inline struct uvc_device *to_uvc(struct usb_function *f)
 struct uvc_file_handle {
        struct v4l2_fh vfh;
        struct uvc_video *device;
+       bool is_uvc_app_handle;
 };
 
 #define to_uvc_file_handle(handle) \

diff --git a/drivers/usb/gadget/function/uvc_v4l2.c b/drivers/usb/gadget/function/uvc_v4l2.c
index 4ca89eab61590d2722fb963c0d75cab5eea90308..197c26f7aec6382cf3019bf32d8254e09c1d4d1c 100644 (file)
--- a/drivers/usb/gadget/function/uvc_v4l2.c
+++ b/drivers/usb/gadget/function/uvc_v4l2.c
@@ -227,17 +227,55 @@ static int
 uvc_v4l2_subscribe_event(struct v4l2_fh *fh,
                         const struct v4l2_event_subscription *sub)
 {
+       struct uvc_device *uvc = video_get_drvdata(fh->vdev);
+       struct uvc_file_handle *handle = to_uvc_file_handle(fh);
+       int ret;
+
        if (sub->type < UVC_EVENT_FIRST || sub->type > UVC_EVENT_LAST)
                return -EINVAL;
 
-       return v4l2_event_subscribe(fh, sub, 2, NULL);
+       if (sub->type == UVC_EVENT_SETUP && uvc->func_connected)
+               return -EBUSY;
+
+       ret = v4l2_event_subscribe(fh, sub, 2, NULL);
+       if (ret < 0)
+               return ret;
+
+       if (sub->type == UVC_EVENT_SETUP) {
+               uvc->func_connected = true;
+               handle->is_uvc_app_handle = true;
+               uvc_function_connect(uvc);
+       }
+
+       return 0;
+}
+
+static void uvc_v4l2_disable(struct uvc_device *uvc)
+{
+       uvc->func_connected = false;
+       uvc_function_disconnect(uvc);
+       uvcg_video_enable(&uvc->video, 0);
+       uvcg_free_buffers(&uvc->video.queue);
 }
 
 static int
 uvc_v4l2_unsubscribe_event(struct v4l2_fh *fh,
                           const struct v4l2_event_subscription *sub)
 {
-       return v4l2_event_unsubscribe(fh, sub);
+       struct uvc_device *uvc = video_get_drvdata(fh->vdev);
+       struct uvc_file_handle *handle = to_uvc_file_handle(fh);
+       int ret;
+
+       ret = v4l2_event_unsubscribe(fh, sub);
+       if (ret < 0)
+               return ret;
+
+       if (sub->type == UVC_EVENT_SETUP && handle->is_uvc_app_handle) {
+               uvc_v4l2_disable(uvc);
+               handle->is_uvc_app_handle = false;
+       }
+
+       return 0;
 }
 
 static long
@@ -292,7 +330,6 @@ uvc_v4l2_open(struct file *file)
        handle->device = &uvc->video;
        file->private_data = &handle->vfh;
 
-       uvc_function_connect(uvc);
        return 0;
 }
 
@@ -304,11 +341,9 @@ uvc_v4l2_release(struct file *file)
        struct uvc_file_handle *handle = to_uvc_file_handle(file->private_data);
        struct uvc_video *video = handle->device;
 
-       uvc_function_disconnect(uvc);
-
        mutex_lock(&video->mutex);
-       uvcg_video_enable(video, 0);
-       uvcg_free_buffers(&video->queue);
+       if (handle->is_uvc_app_handle)
+               uvc_v4l2_disable(uvc);
        mutex_unlock(&video->mutex);
 
        file->private_data = NULL;