From dc887661be33dd88e97bd0baaa899a9bd6d7eb8b Mon Sep 17 00:00:00 2001 From: Sakari Ailus Date: Wed, 27 Sep 2023 14:22:52 +0300 Subject: media: Documentation: Split camera sensor documentation Split camera sensor documentation into user and kernel portions. This should make it easier for the user space developers to find the relevant documentation. Also add a list of exemplary drivers and add imx219 driver to it, besides those that were already mentioned. Signed-off-by: Sakari Ailus Reviewed-by: Laurent Pinchart Reviewed-by: Jacopo Mondi Signed-off-by: Hans Verkuil --- .../userspace-api/media/drivers/camera-sensor.rst | 104 +++++++++++++++++++++ .../userspace-api/media/drivers/index.rst | 1 + Documentation/userspace-api/media/v4l/control.rst | 4 + 3 files changed, 109 insertions(+) create mode 100644 Documentation/userspace-api/media/drivers/camera-sensor.rst (limited to 'Documentation/userspace-api') diff --git a/Documentation/userspace-api/media/drivers/camera-sensor.rst b/Documentation/userspace-api/media/drivers/camera-sensor.rst new file mode 100644 index 000000000000..919a50e8b9d9 --- /dev/null +++ b/Documentation/userspace-api/media/drivers/camera-sensor.rst @@ -0,0 +1,104 @@ +.. SPDX-License-Identifier: GPL-2.0 + +.. _media_using_camera_sensor_drivers: + +Using camera sensor drivers +=========================== + +This section describes common practices for how the V4L2 sub-device interface is +used to control the camera sensor drivers. + +You may also find :ref:`media_writing_camera_sensor_drivers` useful. + +Frame size +---------- + +There are two distinct ways to configure the frame size produced by camera +sensors. + +Freely configurable camera sensor drivers +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Freely configurable camera sensor drivers expose the device's internal +processing pipeline as one or more sub-devices with different cropping and +scaling configurations. The output size of the device is the result of a series +of cropping and scaling operations from the device's pixel array's size. + +An example of such a driver is the CCS driver. + +Register list based drivers +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Register list based drivers generally, instead of able to configure the device +they control based on user requests, are limited to a number of preset +configurations that combine a number of different parameters that on hardware +level are independent. How a driver picks such configuration is based on the +format set on a source pad at the end of the device's internal pipeline. + +Most sensor drivers are implemented this way. + +Frame interval configuration +---------------------------- + +There are two different methods for obtaining possibilities for different frame +intervals as well as configuring the frame interval. Which one to implement +depends on the type of the device. + +Raw camera sensors +~~~~~~~~~~~~~~~~~~ + +Instead of a high level parameter such as frame interval, the frame interval is +a result of the configuration of a number of camera sensor implementation +specific parameters. Luckily, these parameters tend to be the same for more or +less all modern raw camera sensors. + +The frame interval is calculated using the following equation:: + + frame interval = (analogue crop width + horizontal blanking) * + (analogue crop height + vertical blanking) / pixel rate + +The formula is bus independent and is applicable for raw timing parameters on +large variety of devices beyond camera sensors. Devices that have no analogue +crop, use the full source image size, i.e. pixel array size. + +Horizontal and vertical blanking are specified by ``V4L2_CID_HBLANK`` and +``V4L2_CID_VBLANK``, respectively. The unit of the ``V4L2_CID_HBLANK`` control +is pixels and the unit of the ``V4L2_CID_VBLANK`` is lines. The pixel rate in +the sensor's **pixel array** is specified by ``V4L2_CID_PIXEL_RATE`` in the same +sub-device. The unit of that control is pixels per second. + +Register list based drivers need to implement read-only sub-device nodes for the +purpose. Devices that are not register list based need these to configure the +device's internal processing pipeline. + +The first entity in the linear pipeline is the pixel array. The pixel array may +be followed by other entities that are there to allow configuring binning, +skipping, scaling or digital crop, see :ref:`VIDIOC_SUBDEV_G_SELECTION +`. + +USB cameras etc. devices +~~~~~~~~~~~~~~~~~~~~~~~~ + +USB video class hardware, as well as many cameras offering a similar higher +level interface natively, generally use the concept of frame interval (or frame +rate) on device level in firmware or hardware. This means lower level controls +implemented by raw cameras may not be used on uAPI (or even kAPI) to control the +frame interval on these devices. + +Rotation, orientation and flipping +---------------------------------- + +Some systems have the camera sensor mounted upside down compared to its natural +mounting rotation. In such cases, drivers shall expose the information to +userspace with the :ref:`V4L2_CID_CAMERA_SENSOR_ROTATION +` control. + +Sensor drivers shall also report the sensor's mounting orientation with the +:ref:`V4L2_CID_CAMERA_SENSOR_ORIENTATION `. + +Sensor drivers that have any vertical or horizontal flips embedded in the +register programming sequences shall initialize the :ref:`V4L2_CID_HFLIP +` and :ref:`V4L2_CID_VFLIP ` controls with the +values programmed by the register sequences. The default values of these +controls shall be 0 (disabled). Especially these controls shall not be inverted, +independently of the sensor's mounting rotation. diff --git a/Documentation/userspace-api/media/drivers/index.rst b/Documentation/userspace-api/media/drivers/index.rst index 783f92f01a4c..1726f8ec86fa 100644 --- a/Documentation/userspace-api/media/drivers/index.rst +++ b/Documentation/userspace-api/media/drivers/index.rst @@ -32,6 +32,7 @@ For more details see the file COPYING in the source distribution of Linux. :numbered: aspeed-video + camera-sensor ccs cx2341x-uapi dw100 diff --git a/Documentation/userspace-api/media/v4l/control.rst b/Documentation/userspace-api/media/v4l/control.rst index 4463fce694b0..57893814a1e5 100644 --- a/Documentation/userspace-api/media/v4l/control.rst +++ b/Documentation/userspace-api/media/v4l/control.rst @@ -143,9 +143,13 @@ Control IDs recognise the difference between digital and analogue gain use controls ``V4L2_CID_DIGITAL_GAIN`` and ``V4L2_CID_ANALOGUE_GAIN``. +.. _v4l2-cid-hflip: + ``V4L2_CID_HFLIP`` ``(boolean)`` Mirror the picture horizontally. +.. _v4l2-cid-vflip: + ``V4L2_CID_VFLIP`` ``(boolean)`` Mirror the picture vertically. -- cgit