[libcamera-devel] [PATCH v3] v4l2: V4L2CameraProxy: Add support for PREPARE_BUF as one of the supported ioctl

[Vedant Paranjape]

Add support for PREPARE_BUF as one of the ioctl. Since this is a compat
layer, there doesn't seem to be an equivalent to the "transfer ownership
of the buffer to kernel driver" in V4L2Camera class.

To match the error checks done by kernel implementation, we'd have to
check if dmabuf fd is valid and that the buffer size is large enough.
Doing so will not add any particular value to the program as
applications most likely don't depend on these conditions being
handled correctly.

Signed-off-by: Vedant Paranjape <vedantparanjape160201 at gmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 src/v4l2/v4l2_camera_proxy.cpp | 35 +++++++++++++++++++++++++++++++++-
 src/v4l2/v4l2_camera_proxy.h   |  1 +
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/src/v4l2/v4l2_camera_proxy.cpp b/src/v4l2/v4l2_camera_proxy.cpp
index ec6daac605fb..f3470a6d312a 100644
--- a/src/v4l2/v4l2_camera_proxy.cpp
+++ b/src/v4l2/v4l2_camera_proxy.cpp
@@ -559,6 +559,38 @@ int V4L2CameraProxy::vidioc_querybuf(V4L2CameraFile *file, struct v4l2_buffer *a
 	return 0;
 }
 
+int V4L2CameraProxy::vidioc_prepare_buf(V4L2CameraFile *file, struct v4l2_buffer *arg)
+{
+	LOG(V4L2Compat, Debug)
+		<< "[" << file->description() << "] " << __func__
+		<< "(index=" << arg->index << ")";
+
+	if (!hasOwnership(file))
+		return -EBUSY;
+
+	if (arg->index >= bufferCount_)
+		return -EINVAL;
+
+	if (arg->flags & V4L2_BUF_FLAG_REQUEST_FD)
+		return -EINVAL;
+
+	if (!validateBufferType(arg->type) ||
+	    !validateMemoryType(arg->memory))
+		return -EINVAL;
+
+	struct v4l2_buffer &buffer = buffers_[arg->index];
+
+	if (buffer.flags & V4L2_BUF_FLAG_QUEUED ||
+	    buffer.flags & V4L2_BUF_FLAG_PREPARED)
+		return -EINVAL;
+
+	buffer.flags |= V4L2_BUF_FLAG_PREPARED;
+
+	arg->flags = buffer.flags;
+
+	return 0;
+}
+
 int V4L2CameraProxy::vidioc_qbuf(V4L2CameraFile *file, struct v4l2_buffer *arg)
 {
 	LOG(V4L2Compat, Debug)
@@ -627,7 +659,7 @@ int V4L2CameraProxy::vidioc_dqbuf(V4L2CameraFile *file, struct v4l2_buffer *arg,
 
 	struct v4l2_buffer &buf = buffers_[currentBuf_];
 
-	buf.flags &= ~(V4L2_BUF_FLAG_QUEUED | V4L2_BUF_FLAG_DONE);
+	buf.flags &= ~(V4L2_BUF_FLAG_QUEUED | V4L2_BUF_FLAG_DONE | V4L2_BUF_FLAG_PREPARED);
 	buf.length = sizeimage_;
 	*arg = buf;
 
@@ -729,6 +761,7 @@ const std::set<unsigned long> V4L2CameraProxy::supportedIoctls_ = {
 	VIDIOC_S_INPUT,
 	VIDIOC_REQBUFS,
 	VIDIOC_QUERYBUF,
+	VIDIOC_PREPARE_BUF,
 	VIDIOC_QBUF,
 	VIDIOC_DQBUF,
 	VIDIOC_EXPBUF,
diff --git a/src/v4l2/v4l2_camera_proxy.h b/src/v4l2/v4l2_camera_proxy.h
index a38b28c744d3..76ca2d8a5558 100644
--- a/src/v4l2/v4l2_camera_proxy.h
+++ b/src/v4l2/v4l2_camera_proxy.h
@@ -58,6 +58,7 @@ private:
 	int vidioc_s_input(V4L2CameraFile *file, int *arg);
 	int vidioc_reqbufs(V4L2CameraFile *file, struct v4l2_requestbuffers *arg);
 	int vidioc_querybuf(V4L2CameraFile *file, struct v4l2_buffer *arg);
+	int vidioc_prepare_buf(V4L2CameraFile *file, struct v4l2_buffer *arg);
 	int vidioc_qbuf(V4L2CameraFile *file, struct v4l2_buffer *arg);
 	int vidioc_dqbuf(V4L2CameraFile *file, struct v4l2_buffer *arg,
 			 libcamera::Mutex *lock) LIBCAMERA_TSA_REQUIRES(*lock);
-- 
2.25.1