Re: [PATCHv3 7/8] videobuf2: handle V4L2_MEMORY_FLAG_NON_COHERENT flag

Sergey Senozhatsky
2021-07-26T04:20:21Z

On (21/07/26 13:05), Sergey Senozhatsky wrote:
> On (21/07/26 10:40), Sergey Senozhatsky wrote:
> > On (21/07/22 19:33), Dafna Hirschfeld wrote:
> > [..]
> > > > int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
> > > > {
> > > > int ret = vb2_verify_memory_type(q, req->memory, req->type);
> > > > + u32 flags = req->flags;
> > > > fill_buf_caps(q, &req->capabilities);
> > > > - return ret ? ret : vb2_core_reqbufs(q, req->memory, 0, &req->count);
> > > > + validate_memory_flags(q, req->memory, &flags);
> > > > + req->flags = flags;
> > >
> > > you can do instead
> > >
> > > validate_memory_flags(q, req->memory, &req->flags);
> >
> > ->flags are u32 for create-bufs and u8 for reqi-bufs. So `*flags = <value>`
> > can write to ->reserved[] for req-bufs (if the value is huge enough).
>
> I guess ->flags can become u8 for both create-bufs and req-bufs.
> We had ->flags in both structs as u32, but then decided to leave
> some reserved[] space in req-bufs and switched to u8 there.

Something like this

---

diff --git a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
index a048a9f6b7b6..cf633b5a4919 100644
--- a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
+++ b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
@@ -112,13 +112,13 @@ than the number requested.
other changes, then set ``count`` to 0, ``memory`` to
``V4L2_MEMORY_MMAP`` and ``format.type`` to the buffer type.

- * - __u32
+ * - __u8
- ``flags``
- Specifies additional buffer management attributes.
See :ref:`memory-flags`.

- * - __u32
- - ``reserved``\ [6]
+ * - __u8
+ - ``reserved``\ [27]
- A place holder for future extensions. Drivers and applications
must set the array to zero.

diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
index 6edf4508c636..2ae949ec0afa 100644
--- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
+++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
@@ -694,7 +694,7 @@ static void fill_buf_caps(struct vb2_queue *q, u32 *caps)

static void validate_memory_flags(struct vb2_queue *q,
int memory,
- u32 *flags)
+ u8 *flags)
{
if (!q->allow_cache_hints || memory != V4L2_MEMORY_MMAP) {
/*
@@ -711,11 +711,9 @@ static void validate_memory_flags(struct vb2_queue *q,
int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
{
int ret = vb2_verify_memory_type(q, req->memory, req->type);
- u32 flags = req->flags;

fill_buf_caps(q, &req->capabilities);
- validate_memory_flags(q, req->memory, &flags);
- req->flags = flags;
+ validate_memory_flags(q, req->memory, &req->flags);
return ret ? ret : vb2_core_reqbufs(q, req->memory,
req->flags, &req->count);
}
@@ -990,11 +988,9 @@ int vb2_ioctl_reqbufs(struct file *file, void *priv,
{
struct video_device *vdev = video_devdata(file);
int res = vb2_verify_memory_type(vdev->queue, p->memory, p->type);
- u32 flags = p->flags;

fill_buf_caps(vdev->queue, &p->capabilities);
- validate_memory_flags(vdev->queue, p->memory, &flags);
- p->flags = flags;
+ validate_memory_flags(vdev->queue, p->memory, &p->flags);
if (res)
return res;
if (vb2_queue_is_busy(vdev, file))
diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
index 7973aa0465d2..ad4f7cee53f2 100644
--- a/include/uapi/linux/videodev2.h
+++ b/include/uapi/linux/videodev2.h
@@ -2513,8 +2513,8 @@ struct v4l2_create_buffers {
__u32 memory;
struct v4l2_format format;
__u32 capabilities;
- __u32 flags;
- __u32 reserved[6];
+ __u8 flags;
+ __u8 reserved[27];
};

/*