[libcamera-devel] [PATCH v3 0/2] Add read-only flag to ControlInfo

[Kieran Bingham]

This small patch series adds a read-only flag to ControlInfo.  This is used
to test if a control, in particular V4L2_CID_HBLANK, can be written to by
userland.  It replaces the slightly fragile workaround we have right now where
we test if the min and max values of a control are the same to determine if
a control is read-only.

Only modified one ControlInfo constructor is modified which is used by the
V4L2Device class to allow this flag to be set, as setting it for a non-v4l2
control probably does not make sense at this point.

Modifying other ControlInfo constructors fails quite quickly falling
into a range of template issues due to multiple signatures matching.

The alternative here would be to rework this such that the ReadOnly flag
could be set /after/ construction with a setter allowing something like:

V4L2_CTRL_TYPE_INTEGER64:
 		return ControlInfo(static_cast<int64_t>(ctrl.minimum),
 				   static_cast<int64_t>(ctrl.maximum),
-				   static_cast<int64_t>(ctrl.default_value));
+				   static_cast<int64_t>(ctrl.default_value))
					.setReadOnly(ctrl.flags & V4L2_CTRL_FLAG_READ_ONLY);

Of course that feels like it could remove the 'contract' of the read
only property by opening up the ability for a ReadOnly control to have
the ReadOnly flag unset - or by opening up the ability to arbitrarily
affect a 'property' of a ControlInfo after it has been made.


Since v2, I have made the following changes to Naush' patches:
 - Initialised ReadOnly flag as false for ControlInfo(Span<>)
 - Improved documentation

Naushir Patuck (2):
  libcamera: controls: Add read-only flag to ControlInfo
  libcamera:camera_sensor, ipa: raspberrypi: Test readOnly() for HBLANK
    control

 include/libcamera/controls.h    |  5 ++++-
 src/ipa/rpi/common/ipa_base.cpp | 12 +-----------
 src/libcamera/camera_sensor.cpp | 14 ++------------
 src/libcamera/controls.cpp      | 22 ++++++++++++++++++----
 src/libcamera/v4l2_device.cpp   | 12 ++++++++----
 5 files changed, 33 insertions(+), 32 deletions(-)

-- 
2.34.1