Re: [PATCH v7 01/28] v4l2: add restricted memory flags

From: Hans Verkuil
Date: Sat Jul 20 2024 - 05:13:57 EST

Hi Yunfei,

First a high-level comment:

Adding a new V4L2 uAPI also requires patches to v4l-utils, specifically v4l2-ctl
and v4l2-compliance (i.e. new tests are needed for this flag). This will also help
you test the driver.

Some more comments below:

On 20/07/2024 09:15, Yunfei Dong wrote:
> From: Jeffrey Kardatzke <jkardatzke@xxxxxxxxxx>
>
> Adds a V4L2 flag which indicates that a queue is using restricted
> dmabufs and the corresponding capability flag.
>
> Signed-off-by: Jeffrey Kardatzke <jkardatzke@xxxxxxxxxx>
> Signed-off-by: Yunfei Dong <yunfei.dong@xxxxxxxxxxxx>
> [Yunfei: Change reviewer's comments]
> ---
> Documentation/userspace-api/media/v4l/buffer.rst | 10 +++++++++-
> .../userspace-api/media/v4l/vidioc-reqbufs.rst | 6 ++++++
> include/media/videobuf2-core.h | 8 +++++++-
> include/uapi/linux/videodev2.h | 2 ++
> 4 files changed, 24 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/userspace-api/media/v4l/buffer.rst b/Documentation/userspace-api/media/v4l/buffer.rst
> index 52bbee81c080..901eb007aae8 100644
> --- a/Documentation/userspace-api/media/v4l/buffer.rst
> +++ b/Documentation/userspace-api/media/v4l/buffer.rst
> @@ -696,7 +696,7 @@ enum v4l2_memory
>
> .. _memory-flags:
>
> -Memory Consistency Flags
> +Memory Flags
> ------------------------
>
> .. raw:: latex
> @@ -728,6 +728,14 @@ Memory Consistency Flags
> only if the buffer is used for :ref:`memory mapping <mmap>` I/O and the
> queue reports the :ref:`V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS
> <V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS>` capability.
> + * .. _`V4L2-MEMORY-FLAG-RESTRICTED`:
> +
> + - ``V4L2_MEMORY_FLAG_RESTRICTED``
> + - 0x00000002
> + - The queued buffers are expected to be in restricted memory. If not, an
> + error will be returned. This flag can only be used with ``V4L2_MEMORY_DMABUF``.
> + Typically restricted buffers are allocated using a restricted dma-heap. This flag
> + can only be specified if the :ref:`V4L2_BUF_CAP_SUPPORTS_RESTRICTED_MEM` is set.
>
> .. raw:: latex
>
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> index bbc22dd76032..8a264ae08db1 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> @@ -122,6 +122,7 @@ aborting or finishing any DMA in progress, an implicit
> .. _V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS:
> .. _V4L2-BUF-CAP-SUPPORTS-MAX-NUM-BUFFERS:
> .. _V4L2-BUF-CAP-SUPPORTS-REMOVE-BUFS:
> +.. _V4L2-BUF-CAP-SUPPORTS-RESTRICTED_MEM:
>
> .. raw:: latex
>
> @@ -166,6 +167,11 @@ aborting or finishing any DMA in progress, an implicit
> :ref:`V4L2_BUF_FLAG_NO_CACHE_INVALIDATE <V4L2-BUF-FLAG-NO-CACHE-INVALIDATE>`,
> :ref:`V4L2_BUF_FLAG_NO_CACHE_CLEAN <V4L2-BUF-FLAG-NO-CACHE-CLEAN>` and
> :ref:`V4L2_MEMORY_FLAG_NON_COHERENT <V4L2-MEMORY-FLAG-NON-COHERENT>`.
> + * - ``V4L2_BUF_CAP_SUPPORTS_RESTRICTED_MEM``
> + - 0x00000100
> + - This capability is set by the driver to indicate the queue supports
> + restricted memory. See
> + :ref:`V4L2_MEMORY_FLAG_RESTRICTED <V4L2-MEMORY-FLAG-RESTRICTED>`.
>
> .. raw:: latex
>

What is missing in this documentation is what error to expect if you queue a buffer
from non-restricted memory to a driver configured for restricted memory. You probably
want a specific error code for that (EACCES? EPERM?).

Regards,

Hans

> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 955237ac503d..afd497e93a37 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -517,6 +517,9 @@ struct vb2_buf_ops {
> * ->finish().
> * @non_coherent_mem: when set queue will attempt to allocate buffers using
> * non-coherent memory.
> + * @allow_restricted_mem: when set user-space can pass the %V4L2_MEMORY_FLAG_RESTRICTED
> + * flag to indicate the dma bufs are restricted.
> + * @restricted_mem: when set queue will verify that the dma bufs are restricted.
> * @lock: pointer to a mutex that protects the &struct vb2_queue. The
> * driver can set this to a mutex to let the v4l2 core serialize
> * the queuing ioctls. If the driver wants to handle locking
> @@ -621,6 +624,8 @@ struct vb2_queue {
> unsigned int uses_requests:1;
> unsigned int allow_cache_hints:1;
> unsigned int non_coherent_mem:1;
> + unsigned int allow_restricted_mem:1;
> + unsigned int restricted_mem:1;
>
> struct mutex *lock;
> void *owner;
> @@ -792,7 +797,8 @@ void vb2_core_querybuf(struct vb2_queue *q, struct vb2_buffer *vb, void *pb);
> * @q: pointer to &struct vb2_queue with videobuf2 queue.
> * @memory: memory type, as defined by &enum vb2_memory.
> * @flags: auxiliary queue/buffer management flags. Currently, the only
> - * used flag is %V4L2_MEMORY_FLAG_NON_COHERENT.
> + * used flags are %V4L2_MEMORY_FLAG_NON_COHERENT and
> + * %V4L2_MEMORY_FLAG_RESTRICTED.
> * @count: requested buffer count.
> *
> * Videobuf2 core helper to implement VIDIOC_REQBUF() operation. It is called
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 4e91362da6da..c4b1bc10af4c 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -1060,6 +1060,7 @@ struct v4l2_requestbuffers {
> };
>
> #define V4L2_MEMORY_FLAG_NON_COHERENT (1 << 0)
> +#define V4L2_MEMORY_FLAG_RESTRICTED (1 << 1)
>
> /* capabilities for struct v4l2_requestbuffers and v4l2_create_buffers */
> #define V4L2_BUF_CAP_SUPPORTS_MMAP (1 << 0)
> @@ -1071,6 +1072,7 @@ struct v4l2_requestbuffers {
> #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_REMOVE_BUFS (1 << 8)
> +#define V4L2_BUF_CAP_SUPPORTS_RESTRICTED_MEM (1 << 9)
>
> /**
> * struct v4l2_plane - plane info for multi-planar buffers