cam: Add DRM helper classes

To prepare for viewfinder operation through the DRM/KMS API, add a set
of helper classes that encapsulate the libdrm functions.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

3 files changed, 1007 insertions, 0 deletions

diff --git a/src/cam/drm.cpp b/src/cam/drm.cpp
new file mode 100644
index 00000000..da317e27
--- /dev/null
+++ b/src/cam/drm.cpp
@@ -0,0 +1,663 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2021, Ideas on Board Oy
+ *
+ * drm.cpp - DRM/KMS Helpers
+ */
+
+#include "drm.h"
+
+#include <algorithm>
+#include <errno.h>
+#include <fcntl.h>
+#include <iostream>
+#include <set>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#include <libcamera/framebuffer.h>
+#include <libcamera/geometry.h>
+#include <libcamera/pixel_format.h>
+
+#include <libdrm/drm_mode.h>
+
+#include "event_loop.h"
+
+namespace DRM {
+
+Object::Object(Device *dev, uint32_t id, Type type)
+	: id_(id), dev_(dev), type_(type)
+{
+	/* Retrieve properties from the objects that support them. */
+	if (type != TypeConnector && type != TypeCrtc &&
+	    type != TypeEncoder && type != TypePlane)
+		return;
+
+	/*
+	 * We can't distinguish between failures due to the object having no
+	 * property and failures due to other conditions. Assume we use the API
+	 * correctly and consider the object has no property.
+	 */
+	drmModeObjectProperties *properties = drmModeObjectGetProperties(dev->fd(), id, type);
+	if (!properties)
+		return;
+
+	properties_.reserve(properties->count_props);
+	for (uint32_t i = 0; i < properties->count_props; ++i)
+		properties_.emplace_back(properties->props[i],
+					 properties->prop_values[i]);
+
+	drmModeFreeObjectProperties(properties);
+}
+
+Object::~Object()
+{
+}
+
+const Property *Object::property(const std::string &name) const
+{
+	for (const PropertyValue &pv : properties_) {
+		const Property *property = static_cast<const Property *>(dev_->object(pv.id()));
+		if (property && property->name() == name)
+			return property;
+	}
+
+	return nullptr;
+}
+
+const PropertyValue *Object::propertyValue(const std::string &name) const
+{
+	for (const PropertyValue &pv : properties_) {
+		const Property *property = static_cast<const Property *>(dev_->object(pv.id()));
+		if (property && property->name() == name)
+			return &pv;
+	}
+
+	return nullptr;
+}
+
+Property::Property(Device *dev, drmModePropertyRes *property)
+	: Object(dev, property->prop_id, TypeProperty),
+	  name_(property->name), flags_(property->flags),
+	  values_(property->values, property->values + property->count_values),
+	  blobs_(property->blob_ids, property->blob_ids + property->count_blobs)
+{
+	if (drm_property_type_is(property, DRM_MODE_PROP_RANGE))
+		type_ = TypeRange;
+	else if (drm_property_type_is(property, DRM_MODE_PROP_ENUM))
+		type_ = TypeEnum;
+	else if (drm_property_type_is(property, DRM_MODE_PROP_BLOB))
+		type_ = TypeBlob;
+	else if (drm_property_type_is(property, DRM_MODE_PROP_BITMASK))
+		type_ = TypeBitmask;
+	else if (drm_property_type_is(property, DRM_MODE_PROP_OBJECT))
+		type_ = TypeObject;
+	else if (drm_property_type_is(property, DRM_MODE_PROP_SIGNED_RANGE))
+		type_ = TypeSignedRange;
+	else
+		type_ = TypeUnknown;
+
+	for (int i = 0; i < property->count_enums; ++i)
+		enums_[property->enums[i].value] = property->enums[i].name;
+}
+
+Blob::Blob(Device *dev, const libcamera::Span<const uint8_t> &data)
+	: Object(dev, 0, Object::TypeBlob)
+{
+	drmModeCreatePropertyBlob(dev->fd(), data.data(), data.size(), &id_);
+}
+
+Blob::~Blob()
+{
+	if (isValid())
+		drmModeDestroyPropertyBlob(device()->fd(), id());
+}
+
+Mode::Mode(const drmModeModeInfo &mode)
+	: drmModeModeInfo(mode)
+{
+}
+
+std::unique_ptr<Blob> Mode::toBlob(Device *dev) const
+{
+	libcamera::Span<const uint8_t> data{ reinterpret_cast<const uint8_t *>(this),
+					     sizeof(*this) };
+	return std::make_unique<Blob>(dev, data);
+}
+
+Crtc::Crtc(Device *dev, const drmModeCrtc *crtc, unsigned int index)
+	: Object(dev, crtc->crtc_id, Object::TypeCrtc), index_(index)
+{
+}
+
+Encoder::Encoder(Device *dev, const drmModeEncoder *encoder)
+	: Object(dev, encoder->encoder_id, Object::TypeEncoder),
+	  type_(encoder->encoder_type)
+{
+	const std::list<Crtc> &crtcs = dev->crtcs();
+	possibleCrtcs_.reserve(crtcs.size());
+
+	for (const Crtc &crtc : crtcs) {
+		if (encoder->possible_crtcs & (1 << crtc.index()))
+			possibleCrtcs_.push_back(&crtc);
+	}
+
+	possibleCrtcs_.shrink_to_fit();
+}
+
+namespace {
+
+const std::map<uint32_t, const char *> connectorTypeNames{
+	{ DRM_MODE_CONNECTOR_Unknown, "Unknown" },
+	{ DRM_MODE_CONNECTOR_VGA, "VGA" },
+	{ DRM_MODE_CONNECTOR_DVII, "DVI-I" },
+	{ DRM_MODE_CONNECTOR_DVID, "DVI-D" },
+	{ DRM_MODE_CONNECTOR_DVIA, "DVI-A" },
+	{ DRM_MODE_CONNECTOR_Composite, "Composite" },
+	{ DRM_MODE_CONNECTOR_SVIDEO, "S-Video" },
+	{ DRM_MODE_CONNECTOR_LVDS, "LVDS" },
+	{ DRM_MODE_CONNECTOR_Component, "Component" },
+	{ DRM_MODE_CONNECTOR_9PinDIN, "9-Pin-DIN" },
+	{ DRM_MODE_CONNECTOR_DisplayPort, "DP" },
+	{ DRM_MODE_CONNECTOR_HDMIA, "HDMI-A" },
+	{ DRM_MODE_CONNECTOR_HDMIB, "HDMI-B" },
+	{ DRM_MODE_CONNECTOR_TV, "TV" },
+	{ DRM_MODE_CONNECTOR_eDP, "eDP" },
+	{ DRM_MODE_CONNECTOR_VIRTUAL, "Virtual" },
+	{ DRM_MODE_CONNECTOR_DSI, "DSI" },
+	{ DRM_MODE_CONNECTOR_DPI, "DPI" },
+};
+
+} /* namespace */
+
+Connector::Connector(Device *dev, const drmModeConnector *connector)
+	: Object(dev, connector->connector_id, Object::TypeConnector),
+	  type_(connector->connector_type)
+{
+	auto typeName = connectorTypeNames.find(connector->connector_type);
+	if (typeName == connectorTypeNames.end()) {
+		std::cerr
+			<< "Invalid connector type "
+			<< connector->connector_type << std::endl;
+		typeName = connectorTypeNames.find(DRM_MODE_CONNECTOR_Unknown);
+	}
+
+	name_ = std::string(typeName->second) + "-"
+	      + std::to_string(connector->connector_type_id);
+
+	switch (connector->connection) {
+	case DRM_MODE_CONNECTED:
+		status_ = Status::Connected;
+		break;
+
+	case DRM_MODE_DISCONNECTED:
+		status_ = Status::Disconnected;
+		break;
+
+	case DRM_MODE_UNKNOWNCONNECTION:
+	default:
+		status_ = Status::Unknown;
+		break;
+	}
+
+	const std::list<Encoder> &encoders = dev->encoders();
+
+	encoders_.reserve(connector->count_encoders);
+
+	for (int i = 0; i < connector->count_encoders; ++i) {
+		uint32_t encoderId = connector->encoders[i];
+		auto encoder = std::find_if(encoders.begin(), encoders.end(),
+					    [=](const Encoder &e) {
+						    return e.id() == encoderId;
+					    });
+		if (encoder == encoders.end()) {
+			std::cerr
+				<< "Encoder " << encoderId << " not found"
+				<< std::endl;
+			continue;
+		}
+
+		encoders_.push_back(&*encoder);
+	}
+
+	encoders_.shrink_to_fit();
+
+	modes_ = { connector->modes, connector->modes + connector->count_modes };
+}
+
+Plane::Plane(Device *dev, const drmModePlane *plane)
+	: Object(dev, plane->plane_id, Object::TypePlane),
+	  possibleCrtcsMask_(plane->possible_crtcs)
+{
+	formats_ = { plane->formats, plane->formats + plane->count_formats };
+
+	const std::list<Crtc> &crtcs = dev->crtcs();
+	possibleCrtcs_.reserve(crtcs.size());
+
+	for (const Crtc &crtc : crtcs) {
+		if (plane->possible_crtcs & (1 << crtc.index()))
+			possibleCrtcs_.push_back(&crtc);
+	}
+
+	possibleCrtcs_.shrink_to_fit();
+}
+
+bool Plane::supportsFormat(const libcamera::PixelFormat &format) const
+{
+	return std::find(formats_.begin(), formats_.end(), format.fourcc())
+		!= formats_.end();
+}
+
+int Plane::setup()
+{
+	const PropertyValue *pv = propertyValue("type");
+	if (!pv)
+		return -EINVAL;
+
+	switch (pv->value()) {
+	case DRM_PLANE_TYPE_OVERLAY:
+		type_ = TypeOverlay;
+		break;
+
+	case DRM_PLANE_TYPE_PRIMARY:
+		type_ = TypePrimary;
+		break;
+
+	case DRM_PLANE_TYPE_CURSOR:
+		type_ = TypeCursor;
+		break;
+
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+FrameBuffer::FrameBuffer(Device *dev)
+	: Object(dev, 0, Object::TypeFb)
+{
+}
+
+FrameBuffer::~FrameBuffer()
+{
+	for (FrameBuffer::Plane &plane : planes_) {
+		struct drm_gem_close gem_close = {
+			.handle = plane.handle,
+			.pad = 0,
+		};
+		int ret;
+
+		do {
+			ret = ioctl(device()->fd(), DRM_IOCTL_GEM_CLOSE, &gem_close);
+		} while (ret == -1 && (errno == EINTR || errno == EAGAIN));
+
+		if (ret == -1) {
+			ret = -errno;
+			std::cerr
+				<< "Failed to close GEM object: "
+				<< strerror(-ret) << std::endl;
+		}
+	}
+
+	drmModeRmFB(device()->fd(), id());
+}
+
+AtomicRequest::AtomicRequest(Device *dev)
+	: dev_(dev), valid_(true)
+{
+	request_ = drmModeAtomicAlloc();
+	if (!request_)
+		valid_ = false;
+}
+
+AtomicRequest::~AtomicRequest()
+{
+	if (request_)
+		drmModeAtomicFree(request_);
+}
+
+int AtomicRequest::addProperty(const Object *object, const std::string &property,
+			       uint64_t value)
+{
+	if (!valid_)
+		return -EINVAL;
+
+	const Property *prop = object->property(property);
+	if (!prop) {
+		valid_ = false;
+		return -EINVAL;
+	}
+
+	return addProperty(object->id(), prop->id(), value);
+}
+
+int AtomicRequest::addProperty(const Object *object, const std::string &property,
+			       std::unique_ptr<Blob> blob)
+{
+	if (!valid_)
+		return -EINVAL;
+
+	const Property *prop = object->property(property);
+	if (!prop) {
+		valid_ = false;
+		return -EINVAL;
+	}
+
+	int ret = addProperty(object->id(), prop->id(), blob->id());
+	if (ret < 0)
+		return ret;
+
+	blobs_.emplace_back(std::move(blob));
+
+	return 0;
+}
+
+int AtomicRequest::addProperty(uint32_t object, uint32_t property, uint64_t value)
+{
+	int ret = drmModeAtomicAddProperty(request_, object, property, value);
+	if (ret < 0) {
+		valid_ = false;
+		return ret;
+	}
+
+	return 0;
+}
+
+int AtomicRequest::commit(unsigned int flags)
+{
+	if (!valid_)
+		return -EINVAL;
+
+	uint32_t drmFlags = 0;
+	if (flags & FlagAllowModeset)
+		drmFlags |= DRM_MODE_ATOMIC_ALLOW_MODESET;
+	if (flags & FlagAsync)
+		drmFlags |= DRM_MODE_PAGE_FLIP_EVENT | DRM_MODE_ATOMIC_NONBLOCK;
+
+	return drmModeAtomicCommit(dev_->fd(), request_, drmFlags, this);
+}
+
+Device::Device()
+	: fd_(-1)
+{
+}
+
+Device::~Device()
+{
+	if (fd_ != -1)
+		drmClose(fd_);
+}
+
+int Device::init()
+{
+	constexpr size_t NODE_NAME_MAX = sizeof("/dev/dri/card255");
+	char name[NODE_NAME_MAX];
+	int ret;
+
+	/*
+	 * Open the first DRM/KMS device. The libdrm drmOpen*() functions
+	 * require either a module name or a bus ID, which we don't have, so
+	 * bypass them. The automatic module loading and device node creation
+	 * from drmOpen() is of no practical use as any modern system will
+	 * handle that through udev or an equivalent component.
+	 */
+	snprintf(name, sizeof(name), "/dev/dri/card%u", 0);
+	fd_ = open(name, O_RDWR | O_CLOEXEC);
+	if (fd_ < 0) {
+		ret = -errno;
+		std::cerr
+			<< "Failed to open DRM/KMS device " << name << ": "
+			<< strerror(-ret) << std::endl;
+		return ret;
+	}
+
+	/*
+	 * Enable the atomic APIs. This also automatically enables the
+	 * universal planes API.
+	 */
+	ret = drmSetClientCap(fd_, DRM_CLIENT_CAP_ATOMIC, 1);
+	if (ret < 0) {
+		ret = -errno;
+		std::cerr
+			<< "Failed to enable atomic capability: "
+			<< strerror(-ret) << std::endl;
+		return ret;
+	}
+
+	/* List all the resources. */
+	ret = getResources();
+	if (ret < 0)
+		return ret;
+
+	EventLoop::instance()->addEvent(fd_, EventLoop::Read,
+					std::bind(&Device::drmEvent, this));
+
+	return 0;
+}
+
+int Device::getResources()
+{
+	int ret;
+
+	std::unique_ptr<drmModeRes, decltype(&drmModeFreeResources)> resources{
+		drmModeGetResources(fd_),
+		&drmModeFreeResources
+	};
+	if (!resources) {
+		ret = -errno;
+		std::cerr
+			<< "Failed to get DRM/KMS resources: "
+			<< strerror(-ret) << std::endl;
+		return ret;
+	}
+
+	for (int i = 0; i < resources->count_crtcs; ++i) {
+		drmModeCrtc *crtc = drmModeGetCrtc(fd_, resources->crtcs[i]);
+		if (!crtc) {
+			ret = -errno;
+			std::cerr
+				<< "Failed to get CRTC: " << strerror(-ret)
+				<< std::endl;
+			return ret;
+		}
+
+		crtcs_.emplace_back(this, crtc, i);
+		drmModeFreeCrtc(crtc);
+
+		Crtc &obj = crtcs_.back();
+		objects_[obj.id()] = &obj;
+	}
+
+	for (int i = 0; i < resources->count_encoders; ++i) {
+		drmModeEncoder *encoder =
+			drmModeGetEncoder(fd_, resources->encoders[i]);
+		if (!encoder) {
+			ret = -errno;
+			std::cerr
+				<< "Failed to get encoder: " << strerror(-ret)
+				<< std::endl;
+			return ret;
+		}
+
+		encoders_.emplace_back(this, encoder);
+		drmModeFreeEncoder(encoder);
+
+		Encoder &obj = encoders_.back();
+		objects_[obj.id()] = &obj;
+	}
+
+	for (int i = 0; i < resources->count_connectors; ++i) {
+		drmModeConnector *connector =
+			drmModeGetConnector(fd_, resources->connectors[i]);
+		if (!connector) {
+			ret = -errno;
+			std::cerr
+				<< "Failed to get connector: " << strerror(-ret)
+				<< std::endl;
+			return ret;
+		}
+
+		connectors_.emplace_back(this, connector);
+		drmModeFreeConnector(connector);
+
+		Connector &obj = connectors_.back();
+		objects_[obj.id()] = &obj;
+	}
+
+	std::unique_ptr<drmModePlaneRes, decltype(&drmModeFreePlaneResources)> planes{
+		drmModeGetPlaneResources(fd_),
+		&drmModeFreePlaneResources
+	};
+	if (!planes) {
+		ret = -errno;
+		std::cerr
+			<< "Failed to get DRM/KMS planes: "
+			<< strerror(-ret) << std::endl;
+		return ret;
+	}
+
+	for (uint32_t i = 0; i < planes->count_planes; ++i) {
+		drmModePlane *plane =
+			drmModeGetPlane(fd_, planes->planes[i]);
+		if (!plane) {
+			ret = -errno;
+			std::cerr
+				<< "Failed to get plane: " << strerror(-ret)
+				<< std::endl;
+			return ret;
+		}
+
+		planes_.emplace_back(this, plane);
+		drmModeFreePlane(plane);
+
+		Plane &obj = planes_.back();
+		objects_[obj.id()] = &obj;
+	}
+
+	/* Set the possible planes for each CRTC. */
+	for (Crtc &crtc : crtcs_) {
+		for (const Plane &plane : planes_) {
+			if (plane.possibleCrtcsMask_ & (1 << crtc.index()))
+				crtc.planes_.push_back(&plane);
+		}
+	}
+
+	/* Collect all property IDs and create Property instances. */
+	std::set<uint32_t> properties;
+	for (const auto &object : objects_) {
+		for (const PropertyValue &value : object.second->properties())
+			properties.insert(value.id());
+	}
+
+	for (uint32_t id : properties) {
+		drmModePropertyRes *property = drmModeGetProperty(fd_, id);
+		if (!property) {
+			ret = -errno;
+			std::cerr
+				<< "Failed to get property: " << strerror(-ret)
+				<< std::endl;
+			continue;
+		}
+
+		properties_.emplace_back(this, property);
+		drmModeFreeProperty(property);
+
+		Property &obj = properties_.back();
+		objects_[obj.id()] = &obj;
+	}
+
+	/* Finally, perform all delayed setup of mode objects. */
+	for (auto &object : objects_) {
+		ret = object.second->setup();
+		if (ret < 0) {
+			std::cerr
+				<< "Failed to setup object " << object.second->id()
+				<< ": " << strerror(-ret) << std::endl;
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+const Object *Device::object(uint32_t id)
+{
+	const auto iter = objects_.find(id);
+	if (iter == objects_.end())
+		return nullptr;
+
+	return iter->second;
+}
+
+std::unique_ptr<FrameBuffer> Device::createFrameBuffer(
+	const libcamera::FrameBuffer &buffer,
+	const libcamera::PixelFormat &format,
+	const libcamera::Size &size, unsigned int stride)
+{
+	std::unique_ptr<FrameBuffer> fb{ new FrameBuffer(this) };
+
+	uint32_t handles[4] = {};
+	uint32_t pitches[4] = {};
+	uint32_t offsets[4] = {};
+	int ret;
+
+	const std::vector<libcamera::FrameBuffer::Plane> &planes = buffer.planes();
+	fb->planes_.reserve(planes.size());
+
+	unsigned int i = 0;
+	for (const libcamera::FrameBuffer::Plane &plane : planes) {
+		uint32_t handle;
+
+		ret = drmPrimeFDToHandle(fd_, plane.fd.fd(), &handle);
+		if (ret < 0) {
+			ret = -errno;
+			std::cerr
+				<< "Unable to import framebuffer dmabuf: "
+				<< strerror(-ret) << std::endl;
+			return nullptr;
+		}
+
+		fb->planes_.push_back({ handle });
+
+		handles[i] = handle;
+		pitches[i] = stride;
+		offsets[i] = 0; /* TODO */
+		++i;
+	}
+
+	ret = drmModeAddFB2(fd_, size.width, size.height, format.fourcc(), handles,
+			    pitches, offsets, &fb->id_, 0);
+	if (ret < 0) {
+		ret = -errno;
+		std::cerr
+			<< "Failed to add framebuffer: "
+			<< strerror(-ret) << std::endl;
+		return nullptr;
+	}
+
+	return fb;
+}
+
+void Device::drmEvent()
+{
+	drmEventContext ctx{};
+	ctx.version = DRM_EVENT_CONTEXT_VERSION;
+	ctx.page_flip_handler = &Device::pageFlipComplete;
+
+	drmHandleEvent(fd_, &ctx);
+}
+
+void Device::pageFlipComplete([[maybe_unused]] int fd,
+			      [[maybe_unused]] unsigned int sequence,
+			      [[maybe_unused]] unsigned int tv_sec,
+			      [[maybe_unused]] unsigned int tv_usec,
+			      void *user_data)
+{
+	AtomicRequest *request = static_cast<AtomicRequest *>(user_data);
+	request->device()->requestComplete.emit(request);
+}
+
+} /* namespace DRM */
diff --git a/src/cam/drm.h b/src/cam/drm.h
new file mode 100644
index 00000000..ee230402
--- /dev/null
+++ b/src/cam/drm.h
@@ -0,0 +1,331 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2021, Ideas on Board Oy
+ *
+ * drm.h - DRM/KMS Helpers
+ */
+#ifndef __CAM_DRM_H__
+#define __CAM_DRM_H__
+
+#include <list>
+#include <map>
+#include <memory>
+#include <string>
+#include <vector>
+
+#include <libcamera/base/signal.h>
+#include <libcamera/base/span.h>
+
+#include <libdrm/drm.h>
+#include <xf86drm.h>
+#include <xf86drmMode.h>
+
+namespace libcamera {
+class FrameBuffer;
+class PixelFormat;
+class Size;
+} /* namespace libcamera */
+
+namespace DRM {
+
+class Device;
+class Plane;
+class Property;
+class PropertyValue;
+
+class Object
+{
+public:
+	enum Type {
+		TypeCrtc = DRM_MODE_OBJECT_CRTC,
+		TypeConnector = DRM_MODE_OBJECT_CONNECTOR,
+		TypeEncoder = DRM_MODE_OBJECT_ENCODER,
+		TypeMode = DRM_MODE_OBJECT_MODE,
+		TypeProperty = DRM_MODE_OBJECT_PROPERTY,
+		TypeFb = DRM_MODE_OBJECT_FB,
+		TypeBlob = DRM_MODE_OBJECT_BLOB,
+		TypePlane = DRM_MODE_OBJECT_PLANE,
+		TypeAny = DRM_MODE_OBJECT_ANY,
+	};
+
+	Object(Device *dev, uint32_t id, Type type);
+	virtual ~Object();
+
+	Device *device() const { return dev_; }
+	uint32_t id() const { return id_; }
+	Type type() const { return type_; }
+
+	const Property *property(const std::string &name) const;
+	const PropertyValue *propertyValue(const std::string &name) const;
+	const std::vector<PropertyValue> &properties() const { return properties_; }
+
+protected:
+	virtual int setup()
+	{
+		return 0;
+	}
+
+	uint32_t id_;
+
+private:
+	friend Device;
+
+	Device *dev_;
+	Type type_;
+	std::vector<PropertyValue> properties_;
+};
+
+class Property : public Object
+{
+public:
+	enum Type {
+		TypeUnknown = 0,
+		TypeRange,
+		TypeEnum,
+		TypeBlob,
+		TypeBitmask,
+		TypeObject,
+		TypeSignedRange,
+	};
+
+	Property(Device *dev, drmModePropertyRes *property);
+
+	Type type() const { return type_; }
+	const std::string &name() const { return name_; }
+
+	bool isImmutable() const { return flags_ & DRM_MODE_PROP_IMMUTABLE; }
+
+	const std::vector<uint64_t> values() const { return values_; }
+	const std::map<uint32_t, std::string> &enums() const { return enums_; }
+	const std::vector<uint32_t> blobs() const { return blobs_; }
+
+private:
+	Type type_;
+	std::string name_;
+	uint32_t flags_;
+	std::vector<uint64_t> values_;
+	std::map<uint32_t, std::string> enums_;
+	std::vector<uint32_t> blobs_;
+};
+
+class PropertyValue
+{
+public:
+	PropertyValue(uint32_t id, uint64_t value)
+		: id_(id), value_(value)
+	{
+	}
+
+	uint32_t id() const { return id_; }
+	uint32_t value() const { return value_; }
+
+private:
+	uint32_t id_;
+	uint64_t value_;
+};
+
+class Blob : public Object
+{
+public:
+	Blob(Device *dev, const libcamera::Span<const uint8_t> &data);
+	~Blob();
+
+	bool isValid() const { return id() != 0; }
+};
+
+class Mode : public drmModeModeInfo
+{
+public:
+	Mode(const drmModeModeInfo &mode);
+
+	std::unique_ptr<Blob> toBlob(Device *dev) const;
+};
+
+class Crtc : public Object
+{
+public:
+	Crtc(Device *dev, const drmModeCrtc *crtc, unsigned int index);
+
+	unsigned int index() const { return index_; }
+	const std::vector<const Plane *> &planes() const { return planes_; }
+
+private:
+	friend Device;
+
+	unsigned int index_;
+	std::vector<const Plane *> planes_;
+};
+
+class Encoder : public Object
+{
+public:
+	Encoder(Device *dev, const drmModeEncoder *encoder);
+
+	uint32_t type() const { return type_; }
+
+	const std::vector<const Crtc *> &possibleCrtcs() const { return possibleCrtcs_; }
+
+private:
+	uint32_t type_;
+	std::vector<const Crtc *> possibleCrtcs_;
+};
+
+class Connector : public Object
+{
+public:
+	enum Status {
+		Connected,
+		Disconnected,
+		Unknown,
+	};
+
+	Connector(Device *dev, const drmModeConnector *connector);
+
+	uint32_t type() const { return type_; }
+	const std::string &name() const { return name_; }
+
+	Status status() const { return status_; }
+
+	const std::vector<const Encoder *> &encoders() const { return encoders_; }
+	const std::vector<Mode> &modes() const { return modes_; }
+
+private:
+	uint32_t type_;
+	std::string name_;
+	Status status_;
+	std::vector<const Encoder *> encoders_;
+	std::vector<Mode> modes_;
+};
+
+class Plane : public Object
+{
+public:
+	enum Type {
+		TypeOverlay,
+		TypePrimary,
+		TypeCursor,
+	};
+
+	Plane(Device *dev, const drmModePlane *plane);
+
+	Type type() const { return type_; }
+	const std::vector<uint32_t> &formats() const { return formats_; }
+	const std::vector<const Crtc *> &possibleCrtcs() const { return possibleCrtcs_; }
+
+	bool supportsFormat(const libcamera::PixelFormat &format) const;
+
+protected:
+	int setup() override;
+
+private:
+	friend class Device;
+
+	Type type_;
+	std::vector<uint32_t> formats_;
+	std::vector<const Crtc *> possibleCrtcs_;
+	uint32_t possibleCrtcsMask_;
+};
+
+class FrameBuffer : public Object
+{
+public:
+	struct Plane {
+		uint32_t handle;
+	};
+
+	~FrameBuffer();
+
+private:
+	friend class Device;
+
+	FrameBuffer(Device *dev);
+
+	std::vector<Plane> planes_;
+};
+
+class AtomicRequest
+{
+public:
+	enum Flags {
+		FlagAllowModeset = (1 << 0),
+		FlagAsync = (1 << 1),
+	};
+
+	AtomicRequest(Device *dev);
+	~AtomicRequest();
+
+	Device *device() const { return dev_; }
+	bool isValid() const { return valid_; }
+
+	int addProperty(const Object *object, const std::string &property,
+			uint64_t value);
+	int addProperty(const Object *object, const std::string &property,
+			std::unique_ptr<Blob> blob);
+	int commit(unsigned int flags = 0);
+
+private:
+	AtomicRequest(const AtomicRequest &) = delete;
+	AtomicRequest(const AtomicRequest &&) = delete;
+	AtomicRequest &operator=(const AtomicRequest &) = delete;
+	AtomicRequest &operator=(const AtomicRequest &&) = delete;
+
+	int addProperty(uint32_t object, uint32_t property, uint64_t value);
+
+	Device *dev_;
+	bool valid_;
+	drmModeAtomicReq *request_;
+	std::list<std::unique_ptr<Blob>> blobs_;
+};
+
+class Device
+{
+public:
+	Device();
+	~Device();
+
+	int init();
+
+	int fd() const { return fd_; }
+
+	const std::list<Crtc> &crtcs() const { return crtcs_; }
+	const std::list<Encoder> &encoders() const { return encoders_; }
+	const std::list<Connector> &connectors() const { return connectors_; }
+	const std::list<Plane> &planes() const { return planes_; }
+	const std::list<Property> &properties() const { return properties_; }
+
+	const Object *object(uint32_t id);
+
+	std::unique_ptr<FrameBuffer> createFrameBuffer(
+		const libcamera::FrameBuffer &buffer,
+		const libcamera::PixelFormat &format,
+		const libcamera::Size &size, unsigned int stride);
+
+	libcamera::Signal<AtomicRequest *> requestComplete;
+
+private:
+	Device(const Device &) = delete;
+	Device(const Device &&) = delete;
+	Device &operator=(const Device &) = delete;
+	Device &operator=(const Device &&) = delete;
+
+	int getResources();
+
+	void drmEvent();
+	static void pageFlipComplete(int fd, unsigned int sequence,
+				     unsigned int tv_sec, unsigned int tv_usec,
+				     void *user_data);
+
+	int fd_;
+
+	std::list<Crtc> crtcs_;
+	std::list<Encoder> encoders_;
+	std::list<Connector> connectors_;
+	std::list<Plane> planes_;
+	std::list<Property> properties_;
+
+	std::map<uint32_t, Object *> objects_;
+};
+
+} /* namespace DRM */
+
+#endif /* __CAM_DRM_H__ */
diff --git a/src/cam/meson.build b/src/cam/meson.build
index e692ea35..b47add55 100644
--- a/src/cam/meson.build
+++ b/src/cam/meson.build
@@ -19,10 +19,23 @@ cam_sources = files([
     'stream_options.cpp',
 ])
 
+cam_cpp_args = []
+
+libdrm = dependency('libdrm', required : false)
+
+if libdrm.found()
+cam_cpp_args += [ '-DHAVE_KMS' ]
+cam_sources += files([
+    'drm.cpp',
+])
+endif
+
 cam  = executable('cam', cam_sources,
                   dependencies : [
                       libatomic,
                       libcamera_public,
+                      libdrm,
                       libevent,
                   ],
+                  cpp_args : cam_cpp_args,
                   install : true)