Re: [PATCHv2 7/8] videobuf2: handle V4L2_MEMORY_FLAG_NON_COHERENT flag

From: Hans Verkuil
Date: Thu Jun 03 2021 - 07:32:22 EST

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Hi Sergey,

Some comments below:

On 27/04/2021 15:13, Sergey Senozhatsky wrote:
> This patch lets user-space to request a non-coherent memory
> allocation during CREATE_BUFS and REQBUFS ioctl calls.
>
> = CREATE_BUFS
>
> struct v4l2_create_buffers has seven 4-byte reserved areas,
> so reserved[0] is renamed to ->flags. The struct, thus, now
> has six reserved 4-byte regions.
>
> = CREATE_BUFS32
>
> struct v4l2_create_buffers32 has seven 4-byte reserved areas,
> so reserved[0] is renamed to ->flags. The struct, thus, now
> has six reserved 4-byte regions.
>
> = REQBUFS
>
> We use one byte of a 4 byte ->reserved[1] member of struct
> v4l2_requestbuffers. The struct, thus, now has reserved 3 bytes.
>
> Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
> ---
> .../media/v4l/vidioc-create-bufs.rst | 7 ++++-
> .../media/v4l/vidioc-reqbufs.rst | 12 +++++---
> .../media/common/videobuf2/videobuf2-core.c | 4 +--
> .../media/common/videobuf2/videobuf2-v4l2.c | 28 +++++++++++++++++--
> drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 9 +++++-
> drivers/media/v4l2-core/v4l2-ioctl.c | 5 +---
> include/uapi/linux/videodev2.h | 9 ++++--
> 7 files changed, 57 insertions(+), 17 deletions(-)
>
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> index f98f18c9e91c..a048a9f6b7b6 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> @@ -113,7 +113,12 @@ than the number requested.
> ``V4L2_MEMORY_MMAP`` and ``format.type`` to the buffer type.
>
> * - __u32
> - - ``reserved``\ [7]
> + - ``flags``
> + - Specifies additional buffer management attributes.
> + See :ref:`memory-flags`.
> +
> + * - __u32
> + - ``reserved``\ [6]
> - 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 e59306aba2b0..5a047c0ec3e8 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> @@ -104,10 +104,14 @@ aborting or finishing any DMA in progress, an implicit
> ``V4L2_MEMORY_MMAP`` and ``type`` set to the buffer type. This will
> free any previously allocated buffers, so this is typically something
> that will be done at the start of the application.
> - * - __u32
> - - ``reserved``\ [1]
> - - A place holder for future extensions. Drivers and applications
> - must set the array to zero.
> + * - __u8
> + - ``flags``
> + - Specifies additional buffer management attributes.
> + See :ref:`memory-flags`.
> + * - __u8
> + - ``reserved``\ [3]
> + - Reserved for future extensions.
> + -
>
> .. _v4l2-buf-capabilities:
> .. _V4L2-BUF-CAP-SUPPORTS-MMAP:
> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index af4db310cf5e..38505783247e 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -762,7 +762,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
> {
> unsigned int num_buffers, allocated_buffers, num_planes = 0;
> unsigned plane_sizes[VB2_MAX_PLANES] = { };
> - bool coherent_mem = true;
> + bool coherent_mem = !(flags & V4L2_MEMORY_FLAG_NON_COHERENT);
> unsigned int i;
> int ret;
>
> @@ -906,7 +906,7 @@ int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
> {
> unsigned int num_planes = 0, num_buffers, allocated_buffers;
> unsigned plane_sizes[VB2_MAX_PLANES] = { };
> - bool coherent_mem = true;
> + bool coherent_mem = !(flags & V4L2_MEMORY_FLAG_NON_COHERENT);
> int ret;
>
> if (q->num_buffers == VB2_MAX_FRAME) {
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index 1166d5a9291a..8d344335552e 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -692,12 +692,29 @@ static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
> #endif
> }
>
> +static void validate_memory_flags(struct vb2_queue *q,
> + int memory,
> + u32 *flags)
> +{
> + if (!q->allow_cache_hints || memory != V4L2_MEMORY_MMAP) {
> + /*
> + * This needs to clear V4L2_MEMORY_FLAG_NON_COHERENT only,
> + * but in order to avoid bugs we zero out all bits.
> + */
> + *flags = 0;

Wouldn't it make sense to add:

} else {
*flags &= ~V4L2_MEMORY_FLAG_NON_COHERENT;

I.e., clear all unknown flags.

> + }
> +}
> +
> 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;
> + return ret ? ret : vb2_core_reqbufs(q, req->memory,
> + req->flags, &req->count);
> }
> EXPORT_SYMBOL_GPL(vb2_reqbufs);
>
> @@ -729,6 +746,7 @@ int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
> unsigned i;
>
> fill_buf_caps(q, &create->capabilities);
> + validate_memory_flags(q, create->memory, &create->flags);
> create->index = q->num_buffers;
> if (create->count == 0)
> return ret != -EBUSY ? ret : 0;
> @@ -772,7 +790,7 @@ int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
> if (requested_sizes[i] == 0)
> return -EINVAL;
> return ret ? ret : vb2_core_create_bufs(q, create->memory,
> - 0,
> + create->flags,
> &create->count,
> requested_planes,
> requested_sizes);
> @@ -955,13 +973,16 @@ 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;
> if (res)
> return res;
> if (vb2_queue_is_busy(vdev, file))
> return -EBUSY;
> - res = vb2_core_reqbufs(vdev->queue, p->memory, 0, &p->count);
> + res = vb2_core_reqbufs(vdev->queue, p->memory, p->flags, &p->count);
> /* If count == 0, then the owner has released all buffers and he
> is no longer owner of the queue. Otherwise we have a new owner. */
> if (res == 0)
> @@ -979,6 +1000,7 @@ int vb2_ioctl_create_bufs(struct file *file, void *priv,
>
> p->index = vdev->queue->num_buffers;
> fill_buf_caps(vdev->queue, &p->capabilities);
> + validate_memory_flags(vdev->queue, p->memory, &p->flags);
> /*
> * If count == 0, then just check if memory and type are valid.
> * Any -EBUSY result from vb2_verify_memory_type can be mapped to 0.
> diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> index 0ca75f6784c5..1aa9ca3b6ca4 100644
> --- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> +++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> @@ -126,6 +126,9 @@ struct v4l2_format32 {
> * @memory: buffer memory type
> * @format: frame format, for which buffers are requested
> * @capabilities: capabilities of this buffer type.
> + * @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).
> * @reserved: future extensions
> */
> struct v4l2_create_buffers32 {
> @@ -134,7 +137,8 @@ struct v4l2_create_buffers32 {
> __u32 memory; /* enum v4l2_memory */
> struct v4l2_format32 format;
> __u32 capabilities;
> - __u32 reserved[7];
> + __u32 flags;
> + __u32 reserved[6];
> };
>
> static int get_v4l2_format32(struct v4l2_format *p64,
> @@ -182,6 +186,8 @@ static int get_v4l2_create32(struct v4l2_create_buffers *p64,
> if (copy_from_user(p64, p32,
> offsetof(struct v4l2_create_buffers32, format)))
> return -EFAULT;
> + if (copy_from_user(&p64->flags, &p32->flags, sizeof(p32->flags)))
> + return -EFAULT;
> return get_v4l2_format32(&p64->format, &p32->format);
> }
>
> @@ -227,6 +233,7 @@ static int put_v4l2_create32(struct v4l2_create_buffers *p64,
> if (copy_to_user(p32, p64,
> offsetof(struct v4l2_create_buffers32, format)) ||
> put_user(p64->capabilities, &p32->capabilities) ||
> + put_user(p64->flags, &p32->flags) ||
> copy_to_user(p32->reserved, p64->reserved, sizeof(p64->reserved)))
> return -EFAULT;
> return put_v4l2_format32(&p64->format, &p32->format);
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 2673f51aafa4..b1430a741936 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -2003,9 +2003,6 @@ static int v4l_reqbufs(const struct v4l2_ioctl_ops *ops,
>
> if (ret)
> return ret;
> -
> - CLEAR_AFTER_FIELD(p, capabilities);

Shouldn't this be:

CLEAR_AFTER_FIELD(p, flags);

You still need to zero the reserved array, after all.

> -
> return ops->vidioc_reqbufs(file, fh, p);
> }
>
> @@ -2045,7 +2042,7 @@ static int v4l_create_bufs(const struct v4l2_ioctl_ops *ops,
> if (ret)
> return ret;
>
> - CLEAR_AFTER_FIELD(create, capabilities);
> + CLEAR_AFTER_FIELD(create, flags);
>
> v4l_sanitize_format(&create->format);
>
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 15f9c9df35d5..d62a6e4f83a0 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -953,7 +953,8 @@ struct v4l2_requestbuffers {
> __u32 type; /* enum v4l2_buf_type */
> __u32 memory; /* enum v4l2_memory */
> __u32 capabilities;
> - __u32 reserved[1];
> + __u8 flags;
> + __u8 reserved[3];
> };
>
> #define V4L2_MEMORY_FLAG_NON_COHERENT (1 << 0)
> @@ -2494,6 +2495,9 @@ struct v4l2_dbg_chip_info {
> * @memory: enum v4l2_memory; buffer memory type
> * @format: frame format, for which buffers are requested
> * @capabilities: capabilities of this buffer type.
> + * @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).
> * @reserved: future extensions
> */
> struct v4l2_create_buffers {
> @@ -2502,7 +2506,8 @@ struct v4l2_create_buffers {
> __u32 memory;
> struct v4l2_format format;
> __u32 capabilities;
> - __u32 reserved[7];
> + __u32 flags;
> + __u32 reserved[6];
> };
>
> /*
>

Regards,

Hans

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