[PATCH 0/3] media: uvcvideo: Prepare deprecation of nodrop

[PATCH 0/3] media: uvcvideo: Prepare deprecation of nodrop

[Ricardo Ribalda]

We intend to deprecate the nodrop parameter in the future and adopt the
default behaviour of the other media drivers: drop invalid packages.

Make the first step in the deprecation by changing the default value of
the parameter and printing an error message when the value is changed.

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
Ricardo Ribalda (3):
      media: uvcvideo: Swap default value for nodrop module param
      media: uvcvideo: Allow changing noparam on the fly
      media: uvcvideo: Announce the user our deprecation intentions

 drivers/media/usb/uvc/uvc_driver.c | 23 ++++++++++++++++++++---
 drivers/media/usb/uvc/uvc_queue.c  |  6 ++----
 drivers/media/usb/uvc/uvcvideo.h   |  4 +---
 3 files changed, 23 insertions(+), 10 deletions(-)
---
base-commit: d216d9cb4dd854ef0a2ec1701f403facb298af51
change-id: 20241217-uvc-deprecate-fbd6228fa1e2

Best regards,
-- 
Ricardo Ribalda <ribalda@chromium.org>

[PATCH 1/3] media: uvcvideo: Swap default value for nodrop module param

[Ricardo Ribalda]

The module param `nodrop` defines what to do with frames that contain an
error: drop them or sending them to userspace.

The default seems to be to send them to userspace so they can decide
what to do with the frame.

Change the default behaviour of uvcvideo to match the rest of the
drivers and maybe get rid of the module parameter in the future.

Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 drivers/media/usb/uvc/uvc_driver.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index b3c8411dc05c..091145743872 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -32,7 +32,7 @@
 
 unsigned int uvc_clock_param = CLOCK_MONOTONIC;
 unsigned int uvc_hw_timestamps_param;
-unsigned int uvc_no_drop_param;
+unsigned int uvc_no_drop_param = 1;
 static unsigned int uvc_quirks_param = -1;
 unsigned int uvc_dbg_param;
 unsigned int uvc_timeout_param = UVC_CTRL_STREAMING_TIMEOUT;

-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH 2/3] media: uvcvideo: Allow changing noparam on the fly

[Ricardo Ribalda]

Right now the parameter value is read during video_registration and
cannot be changed afterwards, despite its permissions 0644, that makes
the user believe that the value can be written.

The parameter only affects the beviour of uvc_queue_buffer_complete(),
with only one check per buffer.

We can read the value directly from uvc_queue_buffer_complete() and
therefore allowing changing it with sysfs on the fly.

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 drivers/media/usb/uvc/uvc_driver.c | 2 +-
 drivers/media/usb/uvc/uvc_queue.c  | 6 ++----
 drivers/media/usb/uvc/uvcvideo.h   | 4 +---
 3 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index 091145743872..10812a841587 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -1995,7 +1995,7 @@ int uvc_register_video_device(struct uvc_device *dev,
 	int ret;
 
 	/* Initialize the video buffers queue. */
-	ret = uvc_queue_init(queue, type, !uvc_no_drop_param);
+	ret = uvc_queue_init(queue, type);
 	if (ret)
 		return ret;
 
diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
index 26ee85657fc8..ed246d8ff31a 100644
--- a/drivers/media/usb/uvc/uvc_queue.c
+++ b/drivers/media/usb/uvc/uvc_queue.c
@@ -208,8 +208,7 @@ static const struct vb2_ops uvc_meta_queue_qops = {
 	.stop_streaming = uvc_stop_streaming,
 };
 
-int uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type,
-		    int drop_corrupted)
+int uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type)
 {
 	int ret;
 
@@ -239,7 +238,6 @@ int uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type,
 	mutex_init(&queue->mutex);
 	spin_lock_init(&queue->irqlock);
 	INIT_LIST_HEAD(&queue->irqqueue);
-	queue->flags = drop_corrupted ? UVC_QUEUE_DROP_CORRUPTED : 0;
 
 	return 0;
 }
@@ -472,7 +470,7 @@ static void uvc_queue_buffer_complete(struct kref *ref)
 	struct vb2_buffer *vb = &buf->buf.vb2_buf;
 	struct uvc_video_queue *queue = vb2_get_drv_priv(vb->vb2_queue);
 
-	if ((queue->flags & UVC_QUEUE_DROP_CORRUPTED) && buf->error) {
+	if (buf->error && !uvc_no_drop_param) {
 		uvc_queue_buffer_requeue(queue, buf);
 		return;
 	}
diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
index 07f9921d83f2..ebbd8afcf136 100644
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -316,7 +316,6 @@ struct uvc_buffer {
 };
 
 #define UVC_QUEUE_DISCONNECTED		(1 << 0)
-#define UVC_QUEUE_DROP_CORRUPTED	(1 << 1)
 
 struct uvc_video_queue {
 	struct vb2_queue queue;
@@ -674,8 +673,7 @@ extern struct uvc_driver uvc_driver;
 struct uvc_entity *uvc_entity_by_id(struct uvc_device *dev, int id);
 
 /* Video buffers queue management. */
-int uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type,
-		   int drop_corrupted);
+int uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type);
 void uvc_queue_release(struct uvc_video_queue *queue);
 int uvc_request_buffers(struct uvc_video_queue *queue,
 			struct v4l2_requestbuffers *rb);

-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH 3/3] media: uvcvideo: Announce the user our deprecation intentions

[Ricardo Ribalda]

If the user sets the nodrop parameter, print a deprecation warning once.
Hopefully they will come to the mailing list if it is an ABI change.

Now that we have a callback, take this chance to parse the parameter as
a boolean.

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 drivers/media/usb/uvc/uvc_driver.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index 10812a841587..d8e8675dd2cd 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -2424,8 +2424,25 @@ module_param_call(clock, uvc_clock_param_set, uvc_clock_param_get,
 MODULE_PARM_DESC(clock, "Video buffers timestamp clock");
 module_param_named(hwtimestamps, uvc_hw_timestamps_param, uint, 0644);
 MODULE_PARM_DESC(hwtimestamps, "Use hardware timestamps");
-module_param_named(nodrop, uvc_no_drop_param, uint, 0644);
+
+static int param_set_nodrop(const char *val, const struct kernel_param *kp)
+{
+	pr_warn_once("uvcvideo: "
+		     DEPRECATED
+		     "nodrop parameter will be eventually removed.\n");
+	return param_set_bool(val, kp);
+}
+
+static const struct kernel_param_ops param_ops_nodrop = {
+	.set = param_set_nodrop,
+	.get = param_get_uint,
+};
+
+param_check_uint(nodrop, &uvc_no_drop_param);
+module_param_cb(nodrop, &param_ops_nodrop, &uvc_no_drop_param, 0644);
+__MODULE_PARM_TYPE(nodrop, "uint");
 MODULE_PARM_DESC(nodrop, "Don't drop incomplete frames");
+
 module_param_named(quirks, uvc_quirks_param, uint, 0644);
 MODULE_PARM_DESC(quirks, "Forced device quirks");
 module_param_named(trace, uvc_dbg_param, uint, 0644);

-- 
2.47.1.613.gc27f4b7a9f-goog

Re: [PATCH 0/3] media: uvcvideo: Prepare deprecation of nodrop

[Hans de Goede]

Hi Ricardo,

Thank you for working on this.

On 17-Dec-24 10:06 PM, Ricardo Ribalda wrote:
> We intend to deprecate the nodrop parameter in the future and adopt the
> default behaviour of the other media drivers: drop invalid packages.

Actually the default behaviour of other media drivers is:

"return buffers with an error to userspace with V4L2_BUF_FLAG_ERROR set
in v4l2_buffer.flags".

It is not "drop invalid packages". The commit messages of patch 1/3
has some related unclear wording, please fix this.

Looking at this I actually have found what arguably is a bug in
the UVC driver when nodrop is set, or at least something which
we must change before making nodrop=1 the default.

Currently uvc_queue_buffer_complete() looks like this:

static void uvc_queue_buffer_complete(struct kref *ref)
{
        struct uvc_buffer *buf = container_of(ref, struct uvc_buffer, ref);
        struct vb2_buffer *vb = &buf->buf.vb2_buf;
        struct uvc_video_queue *queue = vb2_get_drv_priv(vb->vb2_queue);

        if ((queue->flags & UVC_QUEUE_DROP_CORRUPTED) && buf->error) {
                uvc_queue_buffer_requeue(queue, buf);
                return;
        }

        buf->state = buf->error ? UVC_BUF_STATE_ERROR : UVC_BUF_STATE_DONE;
        vb2_set_plane_payload(&buf->buf.vb2_buf, 0, buf->bytesused);
        vb2_buffer_done(&buf->buf.vb2_buf, VB2_BUF_STATE_DONE);
}

Notice how the last line does not propagate buf->error to the
videobuf2 code, so when nodrop=1 is set then buffers with errors
are not only returned to userspace, they are returned to userspace
without V4L2_BUF_FLAG_ERROR getting set in v4l2_buffer.flags .

The right thing to do in this case is to set V4L2_BUF_FLAG_ERROR
IOW the last line of uvc_queue_buffer_complete() should be changed to:

        vb2_buffer_done(&buf->buf.vb2_buf, buf->error ? VB2_BUF_STATE_ERROR : VB2_BUF_STATE_DONE);

And this should probably be the first patch in a v2 series for this.

Regards,

Hans