[PATCH 0/4] media: Register read-only sub-dev devnode

[Jacopo Mondi <jacopo@jmondi.org>]

Add new functio v4l2_device_register_ro_subdev_nodes() to pair with
v4l2_device_register_subdev_nodes() that allows a bridge driver to register the
device node for its subdevices in read-only mode.

devnode-centric (aka non-MC) bridge drivers control their subdevices through
direct calls to v4l2 subdev operations and do not want userspace to be able
to control the subdevice configuration by calling ioctls on the sub-device
devnode. For this reason, they mostly refrain from registering any devnode at
all for their subdevices.

However it is sometimes required for userspace to access the sub-dev device
nodes to collect information on the actual configuration, without changing
the one currently applied to the device.

This requirement became pressing while working on libcamera on devnode-centric
platforms that do not expose any sub-device for their camera sensor to prevent
userspace from changing their configuration. To allow them to register device
node and being guaranteed to retain control of the subdevice configuration this
series proposes a way to register device nodes in read-only to restrict
access to all ioctls that could potentially affect the sub-dev configuration.

Thanks
   j

Jacopo Mondi (4):
  Documentation: media: Document read-only subdevice
  media: v4l2-dev: Add v4l2_device_register_ro_subdev_node()
  media: bcm2835: Register sensor devnode as read-only
  media: bcm2835: Fix trivial whitespace error

 Documentation/media/kapi/v4l2-subdev.rst      | 38 +++++++++++++++++++
 .../media/uapi/v4l/vidioc-g-dv-timings.rst    |  6 +++
 Documentation/media/uapi/v4l/vidioc-g-std.rst |  6 +++
 .../media/uapi/v4l/vidioc-subdev-g-crop.rst   |  9 +++++
 .../media/uapi/v4l/vidioc-subdev-g-fmt.rst    |  8 ++++
 .../v4l/vidioc-subdev-g-frame-interval.rst    |  8 ++++
 .../uapi/v4l/vidioc-subdev-g-selection.rst    |  8 ++++
 .../media/platform/bcm2835/bcm2835-unicam.c   |  4 +-
 drivers/media/v4l2-core/v4l2-device.c         | 16 +++++++-
 drivers/media/v4l2-core/v4l2-subdev.c         | 19 ++++++++++
 include/media/v4l2-dev.h                      |  7 ++++
 include/media/v4l2-device.h                   | 10 +++++
 12 files changed, 136 insertions(+), 3 deletions(-)

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2.25.1