A long standing issue is how to find the associated media device for
a V4L or DVB device node. This is primarily useful for applications
like v4l2-ctl and v4l2-compliance.
Until recently these applications relied on /sys and the fact that
the media device was accessible in /sys via:
/sys/class/video4linux/videoX/device/mediaY/
But commit ee494cf377e1 ("media: v4l2-device: Link subdevices to their
parent devices if available") broke that scheme for subdevices. That
scheme was rather a hack anyway.
Attempts to report the major/minor number of the media device via the
public API (i.e. by extending VIDIOC_QUERYCAP or VIDIOC_SUBDEV_QUERYCAP)
failed, so this patch series now just adds a media_dev attribute when a
V4L or DVB device node is created. This attribute contains the major:minor
of the media device. It is only created if the device node is actually
associated with a media controller.
The original idea for this v3 was to store the media device minor/major
at the time of the device node registration, however the media device
node is typically created last, so this information isn't known yet.
Instead a new media_device_devt() function was added that returns the
dev_t of the media device node safely.
In addition a patch was added for vim2m to ensure that the v4l2_dev.mdev
is set before video_register_device() to ensure that the media_dev
attribute is created.
This issue was reported by Sebastian Frick:
https://lore.kernel.org/linux-media/20210120183054.5ltnjdtrmumplevt@basti-TUXEDO-Book-XA1510/T/#t
Regards,
Hans
Changes since v2: add new media_device_devt function.
Add vim2m patch: v4l2_dev.mdev was set too late.
Changes since v1: use the is_visible callback to ensure the attribute
is only shown if mdev is non-NULL.
Hans Verkuil (4):
vim2m: intialize the media device earlier
media-device: add media_device_devt function
v4l2-dev: add /sys media_dev attr for V4L2 devices
dvbdev: add /sys media_dev attr for DVB devices
drivers/media/dvb-core/dvbdev.c | 45 +++++++++++++++++++++++++++
drivers/media/mc/mc-device.c | 16 ++++++++++
drivers/media/test-drivers/vim2m.c | 14 +++++----
drivers/media/v4l2-core/v4l2-dev.c | 49 +++++++++++++++++++++++++++++-
include/media/media-device.h | 10 ++++++
5 files changed, 127 insertions(+), 7 deletions(-)
--
2.29.2
