[PATCH v11 44/56] media: core: Report the maximum possible number of buffers for the queue

Benjamin Gaignard
2023-10-12T11:47:14Z

Use one of the struct v4l2_create_buffers reserved bytes to report
the maximum possible number of buffers for the queue.
V4l2 framework set V4L2_BUF_CAP_SUPPORTS_SET_MAX_BUFS flags in queue
capabilities so userland can know when the field is valid.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>

# Conflicts:
# drivers/media/common/videobuf2/videobuf2-v4l2.c
---
.../userspace-api/media/v4l/vidioc-create-bufs.rst | 8 ++++++--
Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst | 1 +
drivers/media/common/videobuf2/videobuf2-v4l2.c | 2 ++
drivers/media/v4l2-core/v4l2-ioctl.c | 4 ++--
include/uapi/linux/videodev2.h | 7 ++++++-
5 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
index a048a9f6b7b6..1a46549e7462 100644
--- a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
+++ b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
@@ -116,9 +116,13 @@ than the number requested.
- ``flags``
- Specifies additional buffer management attributes.
See :ref:`memory-flags`.
-
* - __u32
- - ``reserved``\ [6]
+ - ``max_buffers``
+ - If V4L2_BUF_CAP_SUPPORTS_SET_MAX_BUFS capability flag is set
+ this field indicate the maximum possible number of buffers
+ for this queue.
+ * - __u32
+ - ``reserved``\ [5]
- A place holder for future extensions. Drivers and applications
must set the array to zero.

diff --git a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
index 099fa6695167..0395187e1a5a 100644
--- a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
+++ b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
@@ -120,6 +120,7 @@ aborting or finishing any DMA in progress, an implicit
.. _V4L2-BUF-CAP-SUPPORTS-ORPHANED-BUFS:
.. _V4L2-BUF-CAP-SUPPORTS-M2M-HOLD-CAPTURE-BUF:
.. _V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS:
+.. _V4L2-BUF-CAP-SUPPORTS-SET-MAX-BUFS:

.. raw:: latex

diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
index 799dd43b4aa9..5f4ea4485223 100644
--- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
+++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
@@ -681,6 +681,7 @@ EXPORT_SYMBOL(vb2_querybuf);
static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
{
*caps = V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS;
+ *caps |= V4L2_BUF_CAP_SUPPORTS_SET_MAX_BUFS;
if (q->io_modes & VB2_MMAP)
*caps |= V4L2_BUF_CAP_SUPPORTS_MMAP;
if (q->io_modes & VB2_USERPTR)
@@ -763,6 +764,7 @@ int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
fill_buf_caps(q, &create->capabilities);
validate_memory_flags(q, create->memory, &create->flags);
create->index = vb2_get_num_buffers(q);
+ create->max_buffers = q->max_num_buffers;
if (create->count == 0)
return ret != -EBUSY ? ret : 0;

diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
index 9b1de54ce379..da355355a869 100644
--- a/drivers/media/v4l2-core/v4l2-ioctl.c
+++ b/drivers/media/v4l2-core/v4l2-ioctl.c
@@ -483,9 +483,9 @@ static void v4l_print_create_buffers(const void *arg, bool write_only)
{
const struct v4l2_create_buffers *p = arg;

- pr_cont("index=%d, count=%d, memory=%s, capabilities=0x%08x, ",
+ pr_cont("index=%d, count=%d, memory=%s, capabilities=0x%08x, max buffers=%u",
p->index, p->count, prt_names(p->memory, v4l2_memory_names),
- p->capabilities);
+ p->capabilities, p->max_buffers);
v4l_print_format(&p->format, write_only);
}

diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
index c3d4e490ce7c..ef1402537395 100644
--- a/include/uapi/linux/videodev2.h
+++ b/include/uapi/linux/videodev2.h
@@ -1035,6 +1035,7 @@ struct v4l2_requestbuffers {
#define V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS (1 << 4)
#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_SET_MAX_BUFS (1 << 7)

/**
* struct v4l2_plane - plane info for multi-planar buffers
@@ -2605,6 +2606,9 @@ struct v4l2_dbg_chip_info {
* @flags: additional buffer management attributes (ignored unless the
* queue has V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS capability
* and configured for MMAP streaming I/O).
+ * @max_buffers: if V4L2_BUF_CAP_SUPPORTS_SET_MAX_BUFS capability flag is set
+ * this field indicate the maximum possible number of buffers
+ * for this queue.
* @reserved: future extensions
*/
struct v4l2_create_buffers {
@@ -2614,7 +2618,8 @@ struct v4l2_create_buffers {
struct v4l2_format format;
__u32 capabilities;
__u32 flags;
- __u32 reserved[6];
+ __u32 max_buffers;
+ __u32 reserved[5];
};

/*
--
2.39.2