Re: [PATCH v19 0/9] Add DELETE_BUF ioctl

[Hans Verkuil]

Hi Benjamin,

On 06/02/2024 09:58, Hans Verkuil wrote:
> On 06/02/2024 09:02, Benjamin Gaignard wrote:
>> Unlike when resolution change on keyframes, dynamic resolution change
>> on inter frames doesn't allow to do a stream off/on sequence because
>> it is need to keep all previous references alive to decode inter frames.
>> This constraint have two main problems:
>> - more memory consumption.
>> - more buffers in use.
>> To solve these issue this series introduce DELETE_BUFS ioctl and remove
>> the 32 buffers limit per queue.
> 
> This v19 looks good. There are three outstanding issues that I need to take a
> look at:
> 
> 1) Can we still signal support for DELETE_BUFS in the V4L2_BUF_CAP_ caps?
>    It would be nice to have, but I'm not sure if and how that can be done.

So, I came up with the following patch to add back the V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS
capability. If the DELETE_BUFS ioctl is valid, then it sets this capability
before calling vidioc_reqbufs or vidioc_create_bufs. So right now it will set
this for any queue. If we ever want to disable this for a specific queue, then
either the driver has to override these two ops and clear the flag, or a new
vb2_queue flag (e.g. disable_delete_bufs) is added and vb2_set_flags_and_caps()
will clear that capability based on that flag.

In any case, for now just set it for both queues by default.

If you agree that this is a good way to proceed, then can you incorporate this
into a v20? You can add the documentation for this cap from the v17 version.

Regards,

	Hans

Signed-off-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
---
diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
index 8e437104f9c1..64f2d662d068 100644
--- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
+++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
@@ -685,7 +685,7 @@ static void vb2_set_flags_and_caps(struct vb2_queue *q, u32 memory,
 		*flags &= V4L2_MEMORY_FLAG_NON_COHERENT;
 	}

-	*caps = V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS;
+	*caps |= V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS;
 	if (q->io_modes & VB2_MMAP)
 		*caps |= V4L2_BUF_CAP_SUPPORTS_MMAP;
 	if (q->io_modes & VB2_USERPTR)
diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
index a172d33edd19..45bc705e171e 100644
--- a/drivers/media/v4l2-core/v4l2-ioctl.c
+++ b/drivers/media/v4l2-core/v4l2-ioctl.c
@@ -2100,6 +2100,7 @@ static int v4l_overlay(const struct v4l2_ioctl_ops *ops,
 static int v4l_reqbufs(const struct v4l2_ioctl_ops *ops,
 				struct file *file, void *fh, void *arg)
 {
+	struct video_device *vfd = video_devdata(file);
 	struct v4l2_requestbuffers *p = arg;
 	int ret = check_fmt(file, p->type);

@@ -2108,6 +2109,9 @@ static int v4l_reqbufs(const struct v4l2_ioctl_ops *ops,

 	memset_after(p, 0, flags);

+	if (is_valid_ioctl(vfd, VIDIOC_DELETE_BUFS))
+		p->capabilities = V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS;
+
 	return ops->vidioc_reqbufs(file, fh, p);
 }

@@ -2141,6 +2145,7 @@ static int v4l_dqbuf(const struct v4l2_ioctl_ops *ops,
 static int v4l_create_bufs(const struct v4l2_ioctl_ops *ops,
 				struct file *file, void *fh, void *arg)
 {
+	struct video_device *vfd = video_devdata(file);
 	struct v4l2_create_buffers *create = arg;
 	int ret = check_fmt(file, create->format.type);

@@ -2151,6 +2156,9 @@ static int v4l_create_bufs(const struct v4l2_ioctl_ops *ops,

 	v4l_sanitize_format(&create->format);

+	if (is_valid_ioctl(vfd, VIDIOC_DELETE_BUFS))
+		create->capabilities = V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS;
+
 	ret = ops->vidioc_create_bufs(file, fh, create);

 	if (create->format.type == V4L2_BUF_TYPE_VIDEO_CAPTURE ||
diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
index 03443833aaaa..da307f46f903 100644
--- a/include/uapi/linux/videodev2.h
+++ b/include/uapi/linux/videodev2.h
@@ -1036,6 +1036,7 @@ struct v4l2_requestbuffers {
 #define V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF	(1 << 5)
 #define V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS		(1 << 6)
 #define V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS		(1 << 7)
+#define V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS		(1 << 8)

 /**
  * struct v4l2_plane - plane info for multi-planar buffers