On 10.11.20 16:36, Hans Verkuil wrote:
On 10/11/2020 16:10, Thomas Hämmerle wrote:
On 10.11.20 15:43, Hans Verkuil wrote:
On 10/11/2020 12:53, Thomas Hämmerle wrote:
On 10.11.20 11:31, Hans Verkuil wrote:
On 10/11/2020 09:25, thomas.haemmerle@xxxxxxxxxxxxxx wrote:
From: Thomas Haemmerle <thomas.haemmerle@xxxxxxxxxxxxxx>
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
another process potentially is streaming.
Move activation of UVC function to subscription on UVC_EVENT_SETUP and
keep track of the number of subscribers (limited to 1) because there we
can guarantee for a userspace program utilizing UVC.
Extend the `struct uvc_file_handle` with member `bool connected` to tag
it for a deactivation of the function.
With this a process is able to check capabilities of the v4l2 device
without deactivating the function for another process actually using the
device for UVC streaming.
Signed-off-by: Thomas Haemmerle <thomas.haemmerle@xxxxxxxxxxxxxx>
---
v2:
- fix deadlock in `uvc_v4l2_unsubscribe_event()` (mutex is already
locked in v4l2-core) introduced in v1
- lock mutex in `uvc_v4l2_release()` to suppress ioctls and protect
connected
drivers/usb/gadget/function/uvc.h | 2 +
drivers/usb/gadget/function/uvc_v4l2.c | 56 +++++++++++++++++++++-----
2 files changed, 48 insertions(+), 10 deletions(-)
diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
index 73da4f9a8d4c..0d0bcbffc8fd 100644
--- a/drivers/usb/gadget/function/uvc.h
+++ b/drivers/usb/gadget/function/uvc.h
@@ -117,6 +117,7 @@ struct uvc_device {
enum uvc_state state;
struct usb_function func;
struct uvc_video video;
+ unsigned int connections;
/* Descriptors */
struct {
@@ -147,6 +148,7 @@ static inline struct uvc_device *to_uvc(struct usb_function *f)
struct uvc_file_handle {
struct v4l2_fh vfh;
struct uvc_video *device;
+ bool connected;
};
#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 67922b1355e6..aee4888e17b1 100644
--- a/drivers/usb/gadget/function/uvc_v4l2.c
+++ b/drivers/usb/gadget/function/uvc_v4l2.c
@@ -228,17 +228,57 @@ 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->connections >= 1))
+ return -EBUSY;
+
+ ret = v4l2_event_subscribe(fh, sub, 2, NULL);
+ if (ret < 0)
+ return ret;
+
+ if (sub->type == UVC_EVENT_SETUP) {
+ uvc->connections++;
+ handle->connected = true;
+ uvc_function_connect(uvc);
+ }
This makes no sense. Why would subscribing to a SETUP event
mean that you are 'connected'?
Subscribing to a SETUP does not mean that you are connected - on a
subscription to SETUP we can expect that there is a userspace process,
utilizing UVC -- which is required for the UVC gadget function -- and
everything is ready to enable the function by calling uvc_function_connect.
How about calling it `function_connected`?
Any application can open the device node and subscribe to this event.
This is not a good place to call uvc_function_connect(), it's an abuse of
the V4L2 API.
Of course - any application can subscribe to this event but since the
event is defined in g_uvc.h I thought that a subscription is most likely
done by a UVC application.
I dug a bit more into this (I have very little gadget driver experience),
and isn't calling uvc_function_connect() something that should be done
on the first open? And when the last filehandle is closed, then
uvc_function_disconnect() can be called to clean up?
Isn't the possibility of the delayed activation of the usb function in
composite.c intended to wait for a corresponding userspace application,
which is required to make the gadget work?
If so, a simple open of the v4l2 device does not mean that the gadget is
ready to go: starting pipewire for example results in quering the device
capabilities of all devices. But this does not mean that the gadget will
work.
Therefore I was looking for a place, where we can expect, that the
application opened the device will utilize UVC and found that a
subscription to a UVC specific event is the right place.
That's why I suggested to do this when buffers are allocated. That's when
the application commits resources to actually use the device. Until that
point everything that an application does is just querying or configuring,
but not actually using it.
The userspace application implementations (including the one from
Laurent Pinchart) usually request buffers on the UVC events sent by the
host. Therefore we would run into chicken-and-egg problem.
BTW, Laurent Pinchart who maintains this driver is away for a week, so he
might know more about this when he comes back.
Okay, so I suggest to wait for him.
Thanks for the review so far!
Regards
Thomas
Regards,
Hans
Regards,
Thomas
That would make much more sense. Grep for v4l2_fh_is_singular_file() on how
to do this, quite a few media drivers need this.
Regards,
Hans
It should be possible to open a V4L2 device node any number of times,
and any filehandle can subscribe to any event, but typically once
userspace allocates buffers (VIDIOC_REQBUFS or VIDIOC_CREATE_BUFS)
then that filehandle is marked as the owner of the device and other
open filehandles are no longer allowed to allocate buffers or stream video.
Sure - this can be also done if userspace allocates buffers.
But why does it make more sense to call uvc_function_connect on
VIDIOC_REQBUFS or VIDIOC_CREATE_BUFS instead of subscribtion to a UVC event?
See e.g. drivers/media/common/videobuf2/videobuf2-v4l2.c
and vb2_ioctl_reqbufs and other vb2_ioctl_* functions.
Unfortunately this UVC gadget driver is rather old and is not using
these helper functions.
Running 'v4l2-compliance' will likely fail on a lot of tests for this
driver.
This driver probably could use some TLC.
I totally agree with that, however this change fixes at least one test
of 'v4l2-compliance'.
Currently a running UVC connection can be corrupted by another process
which just opens and closes the device.
Thomas
Regards,
Hans
+
+ return 0;
+}
+
+static void uvc_v4l2_disable(struct uvc_device *uvc)
+{
+ if (--uvc->connections)
+ return;
+
+ 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->connected) {
+ uvc_v4l2_disable(uvc);
+ handle->connected = false;
+ }
+
+ return 0;
}
static long
@@ -293,7 +333,6 @@ uvc_v4l2_open(struct file *file)
handle->device = &uvc->video;
file->private_data = &handle->vfh;
- uvc_function_connect(uvc);
return 0;
}
@@ -303,14 +342,11 @@ uvc_v4l2_release(struct file *file)
struct video_device *vdev = video_devdata(file);
struct uvc_device *uvc = video_get_drvdata(vdev);
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);
- mutex_unlock(&video->mutex);
+ mutex_lock(&uvc->video.mutex);
+ if (handle->connected)
+ uvc_v4l2_disable(uvc);
+ mutex_unlock(&uvc->video.mutex);
file->private_data = NULL;
v4l2_fh_del(&handle->vfh);
