From b409f5f5d1b2caf0eeee9816127649cd2349dbff Mon Sep 17 00:00:00 2001
From: Wim Taymans <wtaymans@redhat.com>
Date: Thu, 7 Nov 2024 15:46:28 +0100
Subject: [PATCH] v4l2: Add mmap fallback when USERPTR is not supported

When we don't support EXPBUF according to the probe, the host will
allocate memory for us. We will then try to use USERPTR to import the
memory into v4l2.

If this is not supported, try to fall back to MMAP support, mmap the
buffers and memcpy the MMAP buffer to the host allocated buffers.
---
 spa/plugins/v4l2/v4l2-source.c |  1 +
 spa/plugins/v4l2/v4l2-utils.c  | 50 +++++++++++++++++++++++++++++-----
 2 files changed, 44 insertions(+), 7 deletions(-)

diff --git a/spa/plugins/v4l2/v4l2-source.c b/spa/plugins/v4l2/v4l2-source.c
index d8a0ca4ff..899a566c2 100644
--- a/spa/plugins/v4l2/v4l2-source.c
+++ b/spa/plugins/v4l2/v4l2-source.c
@@ -58,6 +58,7 @@ struct buffer {
 	struct spa_meta_videotransform *vt;
 	struct v4l2_buffer v4l2_buffer;
 	void *ptr;
+	void *mmap_ptr;
 };
 
 #define MAX_CONTROLS	64
diff --git a/spa/plugins/v4l2/v4l2-utils.c b/spa/plugins/v4l2/v4l2-utils.c
index e7ba279de..c14037d1a 100644
--- a/spa/plugins/v4l2/v4l2-utils.c
+++ b/spa/plugins/v4l2/v4l2-utils.c
@@ -120,7 +120,6 @@ static int spa_v4l2_buffer_recycle(struct impl *this, uint32_t buffer_id)
 		spa_log_error(this->log, "'%s' VIDIOC_QBUF: %m", this->props.device);
 		return -err;
 	}
-
 	return 0;
 }
 
@@ -147,6 +146,8 @@ static int spa_v4l2_clear_buffers(struct impl *this)
 		if (SPA_FLAG_IS_SET(b->flags, BUFFER_FLAG_MAPPED)) {
 			munmap(b->ptr, d[0].maxsize);
 		}
+		if (b->mmap_ptr)
+			munmap(b->mmap_ptr, b->v4l2_buffer.length);
 		if (SPA_FLAG_IS_SET(b->flags, BUFFER_FLAG_ALLOCATED)) {
 			spa_log_debug(this->log, "close %d", (int) d[0].fd);
 			close(d[0].fd);
@@ -1451,12 +1452,15 @@ static int mmap_read(struct impl *this)
 
 	d = b->outbuf->datas;
 	d[0].chunk->offset = 0;
-	d[0].chunk->size = buf.bytesused;
+	d[0].chunk->size = SPA_MIN(buf.bytesused, d[0].maxsize);
 	d[0].chunk->stride = port->fmt.fmt.pix.bytesperline;
 	d[0].chunk->flags = 0;
 	if (buf.flags & V4L2_BUF_FLAG_ERROR)
 		d[0].chunk->flags |= SPA_CHUNK_FLAG_CORRUPTED;
 
+	if (b->mmap_ptr && b->ptr)
+		memcpy(b->ptr, b->mmap_ptr, d[0].chunk->size);
+
 	spa_list_append(&port->queue, &b->link);
 	return 0;
 }
@@ -1541,8 +1545,22 @@ static int spa_v4l2_use_buffers(struct impl *this, struct spa_buffer **buffers,
 	reqbuf.count = n_buffers;
 
 	if (xioctl(dev->fd, VIDIOC_REQBUFS, &reqbuf) < 0) {
-		spa_log_error(this->log, "'%s' VIDIOC_REQBUFS %m", this->props.device);
-		return -errno;
+		if (port->memtype != V4L2_MEMORY_USERPTR) {
+			spa_log_error(this->log, "'%s' VIDIOC_REQBUFS %m", this->props.device);
+			return -errno;
+		}
+		/* some drivers (v4l2loopback) don't support USERPTR
+		 * and so we need to try again with MMAP and memcpy */
+		port->memtype = V4L2_MEMORY_MMAP;
+		spa_zero(reqbuf);
+		reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+		reqbuf.memory = port->memtype;
+		reqbuf.count = n_buffers;
+
+		if (xioctl(dev->fd, VIDIOC_REQBUFS, &reqbuf) < 0) {
+			spa_log_error(this->log, "'%s' VIDIOC_REQBUFS %m", this->props.device);
+			return -errno;
+		}
 	}
 	spa_log_debug(this->log, "got %d buffers", reqbuf.count);
 	if (reqbuf.count < n_buffers) {
@@ -1575,7 +1593,8 @@ static int spa_v4l2_use_buffers(struct impl *this, struct spa_buffer **buffers,
 		b->v4l2_buffer.memory = port->memtype;
 		b->v4l2_buffer.index = i;
 
-		if (port->memtype == V4L2_MEMORY_USERPTR) {
+		if (port->memtype == V4L2_MEMORY_USERPTR ||
+		    port->memtype == V4L2_MEMORY_MMAP) {
 			if (d[0].data == NULL) {
 				void *data;
 
@@ -1593,8 +1612,24 @@ static int spa_v4l2_use_buffers(struct impl *this, struct spa_buffer **buffers,
 			else
 				b->ptr = d[0].data;
 
-			b->v4l2_buffer.m.userptr = (unsigned long) b->ptr;
-			b->v4l2_buffer.length = d[0].maxsize;
+			if (port->memtype == V4L2_MEMORY_USERPTR) {
+				b->v4l2_buffer.m.userptr = (unsigned long) b->ptr;
+				b->v4l2_buffer.length = d[0].maxsize;
+			}
+			else {
+				if (xioctl(dev->fd, VIDIOC_QUERYBUF, &b->v4l2_buffer) < 0) {
+					spa_log_error(this->log, "'%s' VIDIOC_QUERYBUF: %m", this->props.device);
+					return -errno;
+				}
+				b->mmap_ptr = mmap(NULL,
+						b->v4l2_buffer.length,
+						PROT_READ, MAP_PRIVATE,
+						dev->fd, b->v4l2_buffer.m.offset);
+				if (b->mmap_ptr == MAP_FAILED) {
+					spa_log_error(this->log, "'%s' mmap: %m", this->props.device);
+					return -errno;
+				}
+			}
 		}
 		else if (port->memtype == V4L2_MEMORY_DMABUF) {
 			b->v4l2_buffer.m.fd = d[0].fd;
@@ -1806,6 +1841,7 @@ static int spa_v4l2_stream_on(struct impl *this)
 	spa_log_debug(this->log, "starting");
 
 	port->first_buffer = true;
+	mmap_read(this);
 
 	type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 	if (xioctl(dev->fd, VIDIOC_STREAMON, &type) < 0) {