libcamera: Add V4L2Controls

Add libcamera V4L2 control support, implemented using the V4L2 Extended
Control APIs. This patch defines the types used to create and manage
controls.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/libcamera/include/v4l2_controls.h

@@ -0,0 +1,80 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * v4l2_controls.h - V4L2 Controls Support
+ */
+
+#ifndef __LIBCAMERA_V4L2_CONTROLS_H__
+#define __LIBCAMERA_V4L2_CONTROLS_H__
+
+#include <string>
+#include <vector>
+
+#include <stdint.h>
+
+#include <linux/v4l2-controls.h>
+#include <linux/videodev2.h>
+
+namespace libcamera {
+
+class V4L2ControlInfo
+{
+public:
+	V4L2ControlInfo(const struct v4l2_query_ext_ctrl &ctrl);
+
+	unsigned int id() const { return id_; }
+	unsigned int type() const { return type_; }
+	size_t size() const { return size_; }
+	const std::string &name() const { return name_; }
+
+private:
+	unsigned int id_;
+	unsigned int type_;
+	size_t size_;
+	std::string name_;
+};
+
+class V4L2Control
+{
+public:
+	V4L2Control(unsigned int id, int value = 0)
+		: id_(id), value_(value) {}
+
+	int64_t value() const { return value_; }
+	void setValue(int64_t value) { value_ = value; }
+
+	unsigned int id() const { return id_; }
+
+private:
+	unsigned int id_;
+	int64_t value_;
+};
+
+class V4L2ControlList
+{
+public:
+	using iterator = std::vector<V4L2Control>::iterator;
+	using const_iterator = std::vector<V4L2Control>::const_iterator;
+
+	iterator begin() { return controls_.begin(); }
+	const_iterator begin() const { return controls_.begin(); }
+	iterator end() { return controls_.end(); }
+	const_iterator end() const { return controls_.end(); }
+
+	bool empty() const { return controls_.empty(); }
+	std::size_t size() const { return controls_.size(); }
+
+	void clear() { controls_.clear(); }
+	void add(unsigned int id, int64_t value = 0);
+
+	V4L2Control *getByIndex(unsigned int index);
+	V4L2Control *operator[](unsigned int id);
+
+private:
+	std::vector<V4L2Control> controls_;
+};
+
+} /* namespace libcamera */
+
+#endif /* __LIBCAMERA_V4L2_CONTROLS_H__ */

src/libcamera/meson.build

@@ -23,6 +23,7 @@ libcamera_sources = files([
     'stream.cpp',
     'timer.cpp',
     'utils.cpp',
+    'v4l2_controls.cpp',
     'v4l2_device.cpp',
     'v4l2_subdevice.cpp',
     'v4l2_videodevice.cpp',

src/libcamera/v4l2_controls.cpp

@@ -0,0 +1,289 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * v4l2_controls.cpp - V4L2 Controls Support
+ */
+
+#include "v4l2_controls.h"
+
+/**
+ * \file v4l2_controls.h
+ * \brief Support for V4L2 Controls using the V4L2 Extended Controls APIs
+ *
+ * The V4L2 Control API allows application to inspect and modify sets of
+ * configurable parameters on a video device or subdevice. The nature of the
+ * parameters an application can modify using the control framework depends on
+ * what the driver implements support for, and on the characteristics of the
+ * underlying hardware platform. Generally controls are used to modify user
+ * visible settings, such as the image brightness and exposure time, or
+ * non-standard parameters which cannot be controlled through the V4L2 format
+ * negotiation API.
+ *
+ * Controls are identified by a numerical ID, defined by the V4L2 kernel headers
+ * and have an associated type. Each control has a value, which is the data that
+ * can be modified with V4L2Device::setControls() or retrieved with
+ * V4L2Device::getControls().
+ *
+ * The control's type along with the control's flags define the type of the
+ * control's value content. Controls can transport a single data value stored in
+ * variable inside the control, or they might as well deal with more complex
+ * data types, such as arrays of matrices, stored in a contiguous memory
+ * locations associated with the control and called 'the payload'. Such controls
+ * are called 'compound controls' and are currently not supported by the
+ * libcamera V4L2 control framework.
+ *
+ * libcamera implements support for controls using the V4L2 Extended Control
+ * API, which allows future handling of controls with payloads of arbitrary
+ * sizes.
+ *
+ * The libcamera V4L2 Controls framework operates on lists of controls, wrapped
+ * by the V4L2ControlList class, to match the V4L2 extended controls API. The
+ * interface to set and get control is implemented by the V4L2Device class, and
+ * this file only provides the data type definitions.
+ *
+ * \todo Add support for compound controls
+ */
+
+namespace libcamera {
+
+/**
+ * \class V4L2ControlInfo
+ * \brief Information on a V4L2 control
+ *
+ * The V4L2ControlInfo class represents all the information related to a V4L2
+ * control, such as its ID, its type, its user-readable name and the expected
+ * size of its value data.
+ *
+ * V4L2ControlInfo instances are created by inspecting the fieldS of a struct
+ * v4l2_query_ext_ctrl structure, after it has been filled by the device driver
+ * as a consequence of a VIDIOC_QUERY_EXT_CTRL ioctl call.
+ *
+ * This class does not contain the control value, but only static information on
+ * the control, which shall be cached by the caller at initialisation time or
+ * the first time the control information is accessed.
+ */
+
+/**
+ * \brief Construct a V4L2ControlInfo from a struct v4l2_query_ext_ctrl
+ * \param ctrl The struct v4l2_query_ext_ctrl as returned by the kernel
+ */
+V4L2ControlInfo::V4L2ControlInfo(const struct v4l2_query_ext_ctrl &ctrl)
+{
+	id_ = ctrl.id;
+	type_ = ctrl.type;
+	name_ = static_cast<const char *>(ctrl.name);
+	size_ = ctrl.elem_size * ctrl.elems;
+}
+
+/**
+ * \fn V4L2ControlInfo::id()
+ * \brief Retrieve the control ID
+ * \return The V4L2 control ID
+ */
+
+/**
+ * \fn V4L2ControlInfo::type()
+ * \brief Retrieve the control type as defined by V4L2_CTRL_TYPE_*
+ * \return The V4L2 control type
+ */
+
+/**
+ * \fn V4L2ControlInfo::size()
+ * \brief Retrieve the control value data size (in bytes)
+ * \return The V4L2 control value data size
+ */
+
+/**
+ * \fn V4L2ControlInfo::name()
+ * \brief Retrieve the control user readable name
+ * \return The V4L2 control user readable name
+ */
+
+/**
+ * \class V4L2Control
+ * \brief A V4L2 control value
+ *
+ * The V4L2Control class represent the value of a V4L2 control. The class
+ * stores values that have been read from or will be applied to a V4L2 device.
+ *
+ * The value stored in the class instances does not reflect what is actually
+ * applied to the hardware but is a pure software cache optionally initialized
+ * at control creation time and modified by a control read or write operation.
+ *
+ * The write and read controls the V4L2Control class instances are not meant
+ * to be directly used but are instead intended to be grouped in
+ * V4L2ControlList instances, which are then passed as parameters to
+ * V4L2Device::setControls() and V4L2Device::getControls() operations.
+ */
+
+/**
+ * \fn V4L2Control::V4L2Control
+ * \brief Construct a V4L2 control with \a id and \a value
+ * \param id The V4L2 control ID
+ * \param value The control value
+ */
+
+/**
+ * \fn V4L2Control::value()
+ * \brief Retrieve the value of the control
+ *
+ * This method returns the cached control value, initially set by
+ * V4L2ControlList::add() and then updated when the controls are read or
+ * written with V4L2Device::getControls() and V4L2Device::setControls().
+ *
+ * \return The V4L2 control value
+ */
+
+/**
+ * \fn V4L2Control::setValue()
+ * \brief Set the value of the control
+ * \param value The new V4L2 control value
+ *
+ * This method stores the control value, which will be applied to the
+ * device when calling V4L2Device::setControls().
+ */
+
+/**
+ * \fn V4L2Control::id()
+ * \brief Retrieve the control ID this instance refers to
+ * \return The V4L2Control ID
+ */
+
+/**
+ * \class V4L2ControlList
+ * \brief Container of V4L2Control instances
+ *
+ * The V4L2ControlList class works as a container for a list of V4L2Control
+ * instances. The class provides operations to add a new control to the list,
+ * get back a control value, and reset the list of controls it contains.
+ *
+ * In order to set and get controls, user of the libcamera V4L2 control
+ * framework should operate on instances of the V4L2ControlList class, and use
+ * them as argument for the V4L2Device::setControls() and
+ * V4L2Device::getControls() operations, which write and read a list of
+ * controls to or from a V4L2 device (a video device or a subdevice).
+ *
+ * Controls are added to a V4L2ControlList instance with the add() method, with
+ * or without a value.
+ *
+ * To write controls to a device, the controls of interest shall be added with
+ * an initial value by calling V4L2ControlList::add(unsigned int id, int64_t
+ * value) to prepare for a write operation. Once the values of all controls of
+ * interest have been added, the V4L2ControlList instance is passed to the
+ * V4L2Device::setControls(), which sets the controls on the device.
+ *
+ * To read controls from a device, the desired controls are added with
+ * V4L2ControlList::add(unsigned int id) to prepare for a read operation. The
+ * V4L2ControlList instance is then passed to V4L2Device::getControls(), which
+ * reads the controls from the device and updates the values stored in
+ * V4L2ControlList.
+ *
+ * V4L2ControlList instances can be reset to remove all controls they contain
+ * and prepare to be re-used for a new control write/read sequence.
+ */
+
+/**
+ * \typedef V4L2ControlList::iterator
+ * \brief Iterator on the V4L2 controls contained in the instance
+ */
+
+/**
+ * \typedef V4L2ControlList::const_iterator
+ * \brief Const iterator on the V4L2 controls contained in the instance
+ */
+
+/**
+ * \fn iterator V4L2ControlList::begin()
+ * \brief Retrieve an iterator to the first V4L2Control in the instance
+ * \return An iterator to the first V4L2 control
+ */
+
+/**
+ * \fn const_iterator V4L2ControlList::begin() const
+ * \brief Retrieve a constant iterator to the first V4L2Control in the instance
+ * \return A constant iterator to the first V4L2 control
+ */
+
+/**
+ * \fn iterator V4L2ControlList::end()
+ * \brief Retrieve an iterator pointing to the past-the-end V4L2Control in the
+ * instance
+ * \return An iterator to the element following the last V4L2 control in the
+ * instance
+ */
+
+/**
+ * \fn const_iterator V4L2ControlList::end() const
+ * \brief Retrieve a constant iterator pointing to the past-the-end V4L2Control
+ * in the instance
+ * \return A constant iterator to the element following the last V4L2 control
+ * in the instance
+ */
+
+/**
+ * \fn V4L2ControlList::empty()
+ * \brief Verify if the instance does not contain any control
+ * \return True if the instance does not contain any control, false otherwise
+ */
+
+/**
+ * \fn V4L2ControlList::size()
+ * \brief Retrieve the number on controls in the instance
+ * \return The number of V4L2Control stored in the instance
+ */
+
+/**
+ * \fn V4L2ControlList::clear()
+ * \brief Remove all controls in the instance
+ */
+
+/**
+ * \brief Add control with \a id and optional \a value to the instance
+ * \param id The V4L2 control ID (V4L2_CID_*)
+ * \param value The V4L2 control value
+ *
+ * This method adds a new V4L2 control to the V4L2ControlList. The newly
+ * inserted control shall not already be present in the control lists, otherwise
+ * this method, and further use of the control list lead to undefined behaviour.
+ */
+void V4L2ControlList::add(unsigned int id, int64_t value)
+{
+	controls_.emplace_back(id, value);
+}
+
+/**
+ * \brief Retrieve the control at \a index
+ * \param[in] index The control index
+ *
+ * Controls are stored in a V4L2ControlList in order of insertion and this
+ * method retrieves the control at \a index.
+ *
+ * \return A pointer to the V4L2Control at \a index or nullptr if the
+ * index is larger than the number of controls
+ */
+V4L2Control *V4L2ControlList::getByIndex(unsigned int index)
+{
+	if (index >= controls_.size())
+		return nullptr;
+
+	return &controls_[index];
+}
+
+/**
+ * \brief Retrieve the control with \a id
+ * \param[in] id The V4L2 control ID (V4L2_CID_xx)
+ * \return A pointer to the V4L2Control with \a id or nullptr if the
+ * control ID is not part of this instance.
+ */
+V4L2Control *V4L2ControlList::operator[](unsigned int id)
+{
+	for (V4L2Control &ctrl : controls_) {
+		if (ctrl.id() == id)
+			return &ctrl;
+	}
+
+	return nullptr;
+}
+
+} /* namespace libcamera */