linux-kernel - [RFC 0/2] Add standard exposure and gain controls for multiple captures

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Message-ID: <20250710220544.89066-1-mirela.rabulea@nxp.com>
Date: Fri, 11 Jul 2025 01:05:42 +0300
From: Mirela Rabulea <mirela.rabulea@....com>
To: mchehab@...nel.org,
	sakari.ailus@...ux.intel.com,
	hverkuil-cisco@...all.nl,
	laurent.pinchart+renesas@...asonboard.com,
	ribalda@...omium.org,
	jai.luthra@...asonboard.com,
	laurentiu.palcu@....com
Cc: linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	LnxRevLi@....com,
	julien.vuillaumier@....com,
	celine.laurencin@....com
Subject: [RFC 0/2] Add standard exposure and gain controls for multiple captures

Add new standard controls as U32 arrays, for sensors with multiple
captures: V4L2_CID_EXPOSURE_MULTI, V4L2_CID_AGAIN_MULTI and
V4L2_CID_DGAIN_MULTI. These will be particularly useful for sensors
that have multiple captures, but the HDR merge is done inside the sensor,
in the end exposing a single stream, but still requiring AEC control
for all captures.

All controls are in the same class, so they could all be set
atomically via VIDIOC_S_EXT_CTRLS, this could turn out to be
useful in case of sensors with context switching.

Each element of the array will hold an u32 value (exposure or gain)
for one capture. The size of the array is up to the sensor driver which
will implement the controls and initialize them via v4l2_ctrl_new_custom().
With this approach, the user-space will have to set valid values
for all the captures represented in the array.

The v4l2-core only supports one scalar min/max/step value for the
entire array, and each element is validated and adjusted to be within
these bounds in v4l2_ctrl_type_op_validate(). The significance for the
maximum value for the exposure control could be "the max value for the
long exposure" or "the max value for the sum of all exposures". If none
of these is ok, the sensor driver can adjust the values as supported and
the user space can use the TRY operation to query the sensor for the
minimum or maximum values.

Mirela Rabulea (2):
  LF-15161-6: media: Add exposure and gain controls for multiple
    captures
  LF-15161-7: Documentation: media: Describe exposure and gain controls
    for multiple captures

 .../media/v4l/ext-ctrls-image-source.rst             | 12 ++++++++++++
 drivers/media/v4l2-core/v4l2-ctrls-defs.c            |  8 ++++++++
 include/uapi/linux/v4l2-controls.h                   |  3 +++
 3 files changed, 23 insertions(+)

-- 
2.43.0