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>
---
.../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
--
Regards,
Laurent Pinchart
