android: camera_worker: Introduce CameraWorker

The Android camera framework provides for each buffer part of a capture
request an acquisition fence the camera HAL is supposed to wait on
before using the buffer. As the libcamera HAL runs in the camera service
thread, it is not possible to perform a synchronous wait there.

Introduce a CameraWorker class that runs an internal thread to wait
on a set of fences before queueing a capture request to the
libcamera::Camera.

Fences completion is handled through a simple poll, similar in
implementation to the sync_wait() function provided by libdrm.

Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>

src/android/camera_worker.cpp

@@ -0,0 +1,122 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2020, Google Inc.
+ *
+ * camera_worker.cpp - Process capture requests on behalf of the Camera HAL
+ */
+
+#include "camera_worker.h"
+
+#include <errno.h>
+#include <string.h>
+#include <sys/poll.h>
+
+#include "camera_device.h"
+
+using namespace libcamera;
+
+LOG_DECLARE_CATEGORY(HAL);
+
+/*
+ * \class CaptureRequest
+ * \brief Wrap a libcamera::Request associated with buffers and fences
+ *
+ * A CaptureRequest is constructed by the CameraDevice, filled with
+ * buffers and fences provided by the camera3 framework and then processed
+ * by the CameraWorker which queues it to the libcamera::Camera after handling
+ * fences.
+ */
+CaptureRequest::CaptureRequest(libcamera::Camera *camera, uint64_t cookie)
+	: camera_(camera)
+{
+	request_ = camera_->createRequest(cookie);
+}
+
+void CaptureRequest::addBuffer(Stream *stream, FrameBuffer *buffer, int fence)
+{
+	request_->addBuffer(stream, buffer);
+	acquireFences_.push_back(fence);
+}
+
+void CaptureRequest::queue()
+{
+	camera_->queueRequest(request_.get());
+}
+
+/*
+ * \class CameraWorker
+ * \brief Process a CaptureRequest on an internal thread
+ *
+ * The CameraWorker class wraps a Worker that runs on an internal thread
+ * and schedules processing of CaptureRequest through it.
+ */
+CameraWorker::CameraWorker()
+{
+	worker_.moveToThread(&thread_);
+}
+
+void CameraWorker::start()
+{
+	thread_.start();
+}
+
+void CameraWorker::stop()
+{
+	thread_.exit();
+	thread_.wait();
+}
+
+void CameraWorker::queueRequest(CaptureRequest *request)
+{
+	/* Async process the request on the worker which runs its own thread. */
+	worker_.invokeMethod(&Worker::processRequest, ConnectionTypeQueued,
+			     request);
+}
+
+/*
+ * \class CameraWorker::Worker
+ * \brief Process a CaptureRequest handling acquisition fences
+ */
+int CameraWorker::Worker::waitFence(int fence)
+{
+	/*
+	 * \todo Better characterize the timeout. Currently equal to the one
+	 * used by the Rockchip Camera HAL on ChromeOS.
+	 */
+	constexpr unsigned int timeoutMs = 300;
+	struct pollfd fds = { fence, POLLIN, 0 };
+
+	do {
+		int ret = poll(&fds, 1, timeoutMs);
+		if (ret == 0)
+			return -ETIME;
+
+		if (ret > 0) {
+			if (fds.revents & (POLLERR | POLLNVAL))
+				return -EINVAL;
+
+			return 0;
+		}
+	} while (errno == EINTR || errno == EAGAIN);
+
+	return -errno;
+}
+
+void CameraWorker::Worker::processRequest(CaptureRequest *request)
+{
+	/* Wait on all fences before queuing the Request. */
+	for (int fence : request->fences()) {
+		if (fence == -1)
+			continue;
+
+		int ret = waitFence(fence);
+		close(fence);
+		if (ret < 0) {
+			LOG(HAL, Error) << "Failed waiting for fence: "
+					<< fence << ": " << strerror(-ret);
+			return;
+		}
+	}
+
+	request->queue();
+}