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Merged
merged 3 commits into from
Aug 14, 2025
Merged

Support DMA-BUF memory type in buffer queue #41

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8d41b00
Support DMA-BUF memory type in buffer queue
liangchingyun Jun 17, 2025
599a2f9
Add support for selecting memory type (MMAP or DMABUF)
liangchingyun Jul 19, 2025
a3c7c7b
Add README section for DMA-BUF support
liangchingyun Jul 22, 2025
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10 changes: 8 additions & 2 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,7 @@ After running `make`, you should be able to generate the following files:

Before loading this kernel module, you have to satisfy its dependency:
```shell
$ sudo modprobe -a videobuf2_vmalloc videobuf2_v4l2
$ sudo modprobe -a videobuf2_vmalloc videobuf2_v4l2 videobuf2-dma-contig
```

The module can be loaded to Linux kernel by runnning the command:
Expand Down Expand Up @@ -56,9 +56,15 @@ $ sudo ./vcam-util -l
You should get:
```
Available virtual V4L2 compatible devices:
1. fbX(640,480,rgb24) -> /dev/video0
1. fbX(640,480,rgb24,mmap) -> /dev/video0
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@jserv jserv Jul 20, 2025

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Add note for DMA-BUF to illustrate the results.

```

The default memory type is MMAP. You can switch to DMA-BUF using the `-t` option, for example:
```shell
$ sudo ./vcam-util -c -t dmabuf
```
The DMA-BUF framework provides a unified way to share buffers across multiple devices.

You can use this command to check if the driver is ok:
```shell
$ sudo v4l2-compliance -d /dev/videoX -f
Expand Down
2 changes: 2 additions & 0 deletions control.c
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Expand Up @@ -73,6 +73,7 @@ static int control_iocontrol_get_device(struct vcam_device_spec *dev_spec)
dev_spec->width = dev->fb_spec.xres_virtual;
dev_spec->height = dev->fb_spec.yres_virtual;
dev_spec->pix_fmt = dev->fb_spec.pix_fmt;
dev_spec->mem_type = dev->fb_spec.mem_type;
dev_spec->cropratio = dev->fb_spec.cropratio;

strncpy((char *) &dev_spec->fb_node, (const char *) vcamfb_get_devnode(dev),
Expand Down Expand Up @@ -174,6 +175,7 @@ static struct vcam_device_spec default_vcam_spec = {
.height = 480,
.cropratio = {.numerator = 3, .denominator = 4},
.pix_fmt = VCAM_PIXFMT_RGB24,
.mem_type = VCAM_MEMORY_MMAP,
};

int request_vcam_device(struct vcam_device_spec *dev_spec)
Expand Down
3 changes: 3 additions & 0 deletions device.h
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Expand Up @@ -89,6 +89,9 @@ struct vcam_device {
struct v4l2_pix_format output_format;
struct v4l2_pix_format input_format;

/* Memory type */
memtype_t mem_type;

/* Conversion switches */
bool conv_pixfmt_on;
bool conv_res_on;
Expand Down
41 changes: 34 additions & 7 deletions vcam-util.c
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Expand Up @@ -10,14 +10,14 @@

#include "vcam.h"

static const char *short_options = "hcm:r:ls:p:d:";
static const char *short_options = "hcm:r:ls:p:d:t:";

const struct option long_options[] = {
{"help", 0, NULL, 'h'}, {"create", 0, NULL, 'c'},
{"modify", 1, NULL, 'm'}, {"list", 0, NULL, 'l'},
{"size", 1, NULL, 's'}, {"pixfmt", 1, NULL, 'p'},
{"device", 1, NULL, 'd'}, {"remove", 1, NULL, 'r'},
{NULL, 0, NULL, 0}};
{"help", 0, NULL, 'h'}, {"create", 0, NULL, 'c'},
{"modify", 1, NULL, 'm'}, {"list", 0, NULL, 'l'},
{"size", 1, NULL, 's'}, {"pixfmt", 1, NULL, 'p'},
{"device", 1, NULL, 'd'}, {"remove", 1, NULL, 'r'},
{"memtype", 1, NULL, 't'}, {NULL, 0, NULL, 0}};

const char *help =
" -h --help Print this informations.\n"
Expand All @@ -37,6 +37,7 @@ const char *help =
"and apply with crop ratio.\n"
"\n"
" -p --pixfmt pix_fmt Specify pixel format (rgb24,yuyv).\n"
" -t --memtype mem_type Specify memory type (mmap,dmabuf).\n"
" -d --device /dev/* Control device node.\n";

enum ACTION { ACTION_NONE, ACTION_CREATE, ACTION_DESTROY, ACTION_MODIFY };
Expand All @@ -45,6 +46,7 @@ struct vcam_device_spec device_template = {
.width = 640,
.height = 480,
.pix_fmt = VCAM_PIXFMT_RGB24,
.mem_type = VCAM_MEMORY_MMAP,
.video_node = "",
.fb_node = "",
};
Expand Down Expand Up @@ -102,6 +104,14 @@ int determine_pixfmt(char *pixfmt_str)
return -1;
}

int determine_memtype(char *memtype_str)
{
if (!strncmp(memtype_str, "mmap", 4))
return VCAM_MEMORY_MMAP;
if (!strncmp(memtype_str, "dmabuf", 6))
return VCAM_MEMORY_DMABUF;
return -1;
}
int create_device(struct vcam_device_spec *dev)
{
int fd = open(ctl_path, O_RDWR);
Expand All @@ -118,6 +128,9 @@ int create_device(struct vcam_device_spec *dev)
if (!dev->pix_fmt)
dev->pix_fmt = device_template.pix_fmt;

if (!dev->mem_type)
dev->mem_type = device_template.mem_type;

int res = ioctl(fd, VCAM_IOCTL_CREATE_DEVICE, dev);
if (res) {
fprintf(stderr, "Failed to create a new device.\n");
Expand Down Expand Up @@ -170,6 +183,9 @@ int modify_device(struct vcam_device_spec *dev)
if (!dev->pix_fmt)
dev->pix_fmt = orig_dev.pix_fmt;

if (!dev->mem_type)
dev->mem_type = orig_dev.mem_type;

if (!dev->cropratio.numerator || !dev->cropratio.denominator)
dev->cropratio = orig_dev.cropratio;

Expand All @@ -195,10 +211,11 @@ int list_devices()
printf("Available virtual V4L2 compatible devices:\n");
while (!ioctl(fd, VCAM_IOCTL_GET_DEVICE, &dev)) {
dev.idx++;
printf("%d. %s(%d,%d,%d/%d,%s) -> %s\n", dev.idx, dev.fb_node,
printf("%d. %s(%d,%d,%d/%d,%s,%s) -> %s\n", dev.idx, dev.fb_node,
dev.width, dev.height, dev.cropratio.numerator,
dev.cropratio.denominator,
dev.pix_fmt == VCAM_PIXFMT_RGB24 ? "rgb24" : "yuyv",
dev.mem_type == VCAM_MEMORY_MMAP ? "mmap" : "dmabuf",
dev.video_node);
}
close(fd);
Expand Down Expand Up @@ -258,6 +275,16 @@ int main(int argc, char *argv[])
dev.pix_fmt = (char) tmp;
printf("Setting pixel format to %s.\n", optarg);
break;
case 't':
tmp = determine_memtype(optarg);
if (tmp < 0) {
fprintf(stderr, "Failed to recognize memory type %s.\n",
optarg);
exit(-1);
}
dev.mem_type = (char) tmp;
printf("Setting memory type to %s.\n", optarg);
break;
case 'd':
printf("Using device %s.\n", optarg);
strncpy(ctl_path, optarg, sizeof(ctl_path) - 1);
Expand Down
2 changes: 2 additions & 0 deletions vcam.h
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Expand Up @@ -10,6 +10,7 @@
#define VCAM_IOCTL_MODIFY_SETTING 0x555

typedef enum { VCAM_PIXFMT_RGB24 = 0x01, VCAM_PIXFMT_YUYV = 0x02 } pixfmt_t;
typedef enum { VCAM_MEMORY_MMAP = 0, VCAM_MEMORY_DMABUF = 2 } memtype_t;

struct crop_ratio {
__u32 numerator;
Expand All @@ -27,6 +28,7 @@ struct vcam_device_spec {
struct crop_ratio cropratio;

pixfmt_t pix_fmt;
memtype_t mem_type;
char video_node[64];
char fb_node[64];
};
Expand Down
32 changes: 30 additions & 2 deletions videobuf.c
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Expand Up @@ -3,6 +3,7 @@
#include <linux/spinlock.h>
#include <linux/vmalloc.h>
#include <media/videobuf2-core.h>
#include <media/videobuf2-dma-contig.h>
#include <media/videobuf2-vmalloc.h>

#include "videobuf.h"
Expand Down Expand Up @@ -114,6 +115,23 @@ static void vcam_outbuf_unlock(struct vb2_queue *vq)
mutex_unlock(&dev->vcam_mutex);
}

static int vcam_buf_init(struct vb2_buffer *vb)
{
struct vcam_out_buffer *buf =
container_of(vb, struct vcam_out_buffer, vb.vb2_buf);

buf->filled = 0;
INIT_LIST_HEAD(&buf->list);

pr_debug("vcam_buf_init: buffer initialized\n");
return 0;
}

static void vcam_buf_cleanup(struct vb2_buffer *vb)
{
pr_debug("vcam_buf_cleanup called\n");
}

static const struct vb2_ops vcam_vb2_ops = {
.queue_setup = vcam_out_queue_setup,
.buf_prepare = vcam_out_buffer_prepare,
Expand All @@ -122,19 +140,29 @@ static const struct vb2_ops vcam_vb2_ops = {
.stop_streaming = vcam_stop_streaming,
.wait_prepare = vcam_outbuf_unlock,
.wait_finish = vcam_outbuf_lock,
.buf_init = vcam_buf_init,
.buf_cleanup = vcam_buf_cleanup,
};

int vcam_out_videobuf2_setup(struct vcam_device *dev)
{
struct vb2_queue *q = &dev->vb_out_vidq;

q->type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
q->io_modes = VB2_MMAP | VB2_USERPTR | VB2_READ;
q->io_modes = VB2_MMAP | VB2_USERPTR | VB2_READ | VB2_DMABUF;
q->drv_priv = dev;
q->buf_struct_size = sizeof(struct vcam_out_buffer);
q->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
q->ops = &vcam_vb2_ops;
q->mem_ops = &vb2_vmalloc_memops;
pr_info("memory type %d\n", dev->mem_type);
switch (dev->mem_type) {
case VCAM_MEMORY_MMAP:
q->mem_ops = &vb2_vmalloc_memops;
break;
case VCAM_MEMORY_DMABUF:
q->mem_ops = &vb2_dma_contig_memops;
break;
}
#if LINUX_VERSION_CODE >= KERNEL_VERSION(6, 8, 0)
q->min_queued_buffers = 2;
#else
Expand Down
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