Hi Laurent,
On Thu, Mar 19, 2020 at 02:46:58AM +0200, Laurent Pinchart wrote:
> The VIDIOC_ENUM_FMT ioctl enumerates all formats supported by a video
> node. For MC-centric devices, its behaviour has always been ill-defined,
> with drivers implementing one of the following behaviours:
>
> - No support for VIDIOC_ENUM_FMT at all
> - Enumerating all formats supported by the video node, regardless of the
> configuration of the pipeline
> - Enumerating formats supported by the video node for the active
> configuration of the connected subdevice
>
> The first behaviour is obviously useless for applications. The second
> behaviour provides the most information, but doesn't offer a way to find
> what formats are compatible with a given pipeline configuration. The
> third behaviour fixes that, but with the drawback that applications
> can't enumerate all supported formats anymore, and have to modify the
> active configuration of the pipeline to enumerate formats.
>
> The situation is messy as none of the implemented behaviours are ideal,
> and userspace can't predict what will happen as the behaviour is
> driver-specific.
>
> To fix this, let's extend the VIDIOC_ENUM_FMT with a missing capability:
> enumerating pixel formats for a given media bus code. The media bus code
> is passed through the v4l2_fmtdesc structure in a new mbus_code field
> (repurposed from the reserved fields). With this capability in place,
> applications can enumerate pixel formats for a given media bus code
> without modifying the active configuration of the device.
>
> The current behaviour of the ioctl is preserved when the new mbus_code
> field is set to 0, ensuring compatibility with existing userspace. The
> API extension is documented as mandatory for MC-centric devices (as
> advertised through the V4L2_CAP_IO_MC capability), allowing applications
> and compliance tools to easily determine the availability of the
> VIDIOC_ENUM_FMT extension.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Acked-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
I'd address setting the reserved fields explicitly in a separate patch,
simply by removing them. As another field in the struct is assigned, the
memory is zeroed and explicit assignment is redundant.
> ---
> .../media/uapi/v4l/vidioc-enum-fmt.rst | 19 +++++++++++++++----
> drivers/media/v4l2-core/v4l2-ioctl.c | 13 +++++++++++--
> include/uapi/linux/videodev2.h | 3 ++-
> 3 files changed, 28 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/media/uapi/v4l/vidioc-enum-fmt.rst b/Documentation/media/uapi/v4l/vidioc-enum-fmt.rst
> index 8ca6ab701e4a..82792d8e910b 100644
> --- a/Documentation/media/uapi/v4l/vidioc-enum-fmt.rst
> +++ b/Documentation/media/uapi/v4l/vidioc-enum-fmt.rst
> @@ -48,10 +48,21 @@ one until ``EINVAL`` is returned. If applicable, drivers shall return
> formats in preference order, where preferred formats are returned before
> (that is, with lower ``index`` value) less-preferred formats.
>
> -.. note::
> -
> - After switching input or output the list of enumerated image
> - formats may be different.
> +If the driver doesn't advertise the ``V4L2_CAP_IO_MC``
> +:ref:`device-capabilities <capability>`, applications shall initialize the
> +``mbus_code`` field to zero. Drivers shall enumerate all image formats supported
> +by the device. The enumerated formats may depend on the active input or output
> +of the device.
> +
> +If the driver advertises the ``V4L2_CAP_IO_MC`` :ref:`device-capabilities
> +<capability>`, applications may initialize the ``mbus_code`` to a valid
> +:ref:`v4l2_mbus_pixelcode <media bus format code>`. If the ``mbus_code` field
> +is not zero, drivers shall restrict enumeration to only the image formats that
> +can produce (for video output devices) or be produced from (for video capture
> +devices) that media bus code. Regardless of the value of the ``mbus_code``
> +field, the enumerated image formats shall not depend on the active
> +configuration of the video device or device pipeline. Enumeration shall
> +otherwise operate as previously described.
>
>
> .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 3545a8adf844..b55603964abd 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -264,12 +264,13 @@ static void v4l_print_fmtdesc(const void *arg, bool write_only)
> {
> const struct v4l2_fmtdesc *p = arg;
>
> - pr_cont("index=%u, type=%s, flags=0x%x, pixelformat=%c%c%c%c, description='%.*s'\n",
> + pr_cont("index=%u, type=%s, flags=0x%x, pixelformat=%c%c%c%c, mbus_code=0x%04x, description='%.*s'\n",
> p->index, prt_names(p->type, v4l2_type_names),
> p->flags, (p->pixelformat & 0xff),
> (p->pixelformat >> 8) & 0xff,
> (p->pixelformat >> 16) & 0xff,
> (p->pixelformat >> 24) & 0xff,
> + p->mbus_code,
> (int)sizeof(p->description), p->description);
> }
>
> @@ -1467,12 +1468,20 @@ static int v4l_enum_fmt(const struct v4l2_ioctl_ops *ops,
> struct video_device *vdev = video_devdata(file);
> struct v4l2_fmtdesc *p = arg;
> int ret = check_fmt(file, p->type);
> + u32 mbus_code;
> u32 cap_mask;
>
> if (ret)
> return ret;
> ret = -EINVAL;
>
> + if (p->mbus_code && !(vdev->device_caps & V4L2_CAP_IO_MC))
> + return -EINVAL;
> +
> + mbus_code = p->mbus_code;
> + CLEAR_AFTER_FIELD(p, type);
> + p->mbus_code = mbus_code;
> +
> switch (p->type) {
> case V4L2_BUF_TYPE_VIDEO_CAPTURE:
> case V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE:
> @@ -2752,7 +2761,7 @@ DEFINE_V4L_STUB_FUNC(dv_timings_cap)
>
> static const struct v4l2_ioctl_info v4l2_ioctls[] = {
> IOCTL_INFO(VIDIOC_QUERYCAP, v4l_querycap, v4l_print_querycap, 0),
> - IOCTL_INFO(VIDIOC_ENUM_FMT, v4l_enum_fmt, v4l_print_fmtdesc, INFO_FL_CLEAR(v4l2_fmtdesc, type)),
> + IOCTL_INFO(VIDIOC_ENUM_FMT, v4l_enum_fmt, v4l_print_fmtdesc, 0),
> IOCTL_INFO(VIDIOC_G_FMT, v4l_g_fmt, v4l_print_format, 0),
> IOCTL_INFO(VIDIOC_S_FMT, v4l_s_fmt, v4l_print_format, INFO_FL_PRIO),
> IOCTL_INFO(VIDIOC_REQBUFS, v4l_reqbufs, v4l_print_requestbuffers, INFO_FL_PRIO | INFO_FL_QUEUE),
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index c793263a3705..0ece960844a5 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -779,7 +779,8 @@ struct v4l2_fmtdesc {
> __u32 flags;
> __u8 description[32]; /* Description string */
> __u32 pixelformat; /* Format fourcc */
> - __u32 reserved[4];
> + __u32 mbus_code; /* Media bus code */
> + __u32 reserved[3];
> };
>
> #define V4L2_FMT_FLAG_COMPRESSED 0x0001
--
Kind regards,
Sakari Ailus
