[FFmpeg-devel] [EXT] Re: [PATCH v1 2/2] avcodec/v4l2_buffer: export v4l2 buffer dma-buf

[Ming Qian]

> -----Original Message-----
> From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf Of
> Ming Qian
> Sent: Monday, November 15, 2021 10:49 AM
> To: FFmpeg development discussions and patches <ffmpeg-devel at ffmpeg.org>
> Subject: Re: [FFmpeg-devel] [EXT] Re: [PATCH v1 2/2] avcodec/v4l2_buffer:
> export v4l2 buffer dma-buf
> 
> Caution: EXT Email
> 
> > -----Original Message-----
> > From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf
> > Of Lynne
> > Sent: Friday, November 12, 2021 4:50 PM
> > To: FFmpeg development discussions and patches
> > <ffmpeg-devel at ffmpeg.org>
> > Subject: [EXT] Re: [FFmpeg-devel] [PATCH v1 2/2] avcodec/v4l2_buffer:
> > export
> > v4l2 buffer dma-buf
> >
> > Caution: EXT Email
> >
> > 12 Nov 2021, 09:36 by ming.qian at nxp.com:
> >
> > > Signed-off-by: Ming Qian <ming.qian at nxp.com>
> > > ---
> > >  libavcodec/v4l2_buffers.c | 14 ++++++++++++++
> > > libavcodec/v4l2_buffers.h |  1 +  libavcodec/v4l2_context.c |  4
> > > ++++
> > >  3 files changed, 19 insertions(+)
> > >
> > > diff --git a/libavcodec/v4l2_buffers.c b/libavcodec/v4l2_buffers.c
> > > index 4b2679eb3814..efa42f4c58ea 100644
> > > --- a/libavcodec/v4l2_buffers.c
> > > +++ b/libavcodec/v4l2_buffers.c
> > > @@ -21,6 +21,9 @@
> > >  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
> > > 02110-1301 USA  */
> > >
> > > +#ifndef _GNU_SOURCE
> > > +#define _GNU_SOURCE
> > > +#endif
> > >  #include <linux/videodev2.h>
> > >  #include <sys/ioctl.h>
> > >  #include <sys/mman.h>
> > > @@ -267,6 +270,8 @@ static int v4l2_buf_to_bufref(V4L2Buffer *in,
> > > int plane, AVBufferRef **buf)  if (!*buf)  return AVERROR(ENOMEM);
> > >
> > > +    if (in->plane_info[plane].dmafd >= 0)
> > > +        av_buffer_set_dma_buf(*buf, in->plane_info[plane].dmafd);
> > >  ret = v4l2_buf_increase_ref(in);
> > >  if (ret)
> > >  av_buffer_unref(buf);
> > > @@ -494,6 +499,7 @@ int ff_v4l2_buffer_avpkt_to_buf(const AVPacket
> > > *pkt, V4L2Buffer *out)  int ff_v4l2_buffer_initialize(V4L2Buffer*
> > > avbuf, int index)  {  V4L2Context *ctx = avbuf->context;
> > > +    struct v4l2_exportbuffer exp;
> > >  int ret, i;
> > >
> > >  avbuf->buf.memory = V4L2_MEMORY_MMAP; @@ -539,6 +545,14 @@
> > int
> > > ff_v4l2_buffer_initialize(V4L2Buffer* avbuf, int index)
> > >
> > >  if (avbuf->plane_info[i].mm_addr == MAP_FAILED)  return
> > > AVERROR(ENOMEM);
> > > +
> > > +        exp.type = ctx->type;
> > > +        exp.index = avbuf->buf.index;
> > > +        exp.plane = i;
> > > +        exp.fd = -1;
> > > +        exp.flags = O_CLOEXEC | O_RDWR;
> > > +        ioctl(buf_to_m2mctx(avbuf)->fd, VIDIOC_EXPBUF, &exp);
> > > +        avbuf->plane_info[i].dmafd = exp.fd;
> > >  }
> > >
> > >  avbuf->status = V4L2BUF_AVAILABLE;
> > > diff --git a/libavcodec/v4l2_buffers.h b/libavcodec/v4l2_buffers.h
> > > index 3d2ff1b9a5d7..74550544e0eb 100644
> > > --- a/libavcodec/v4l2_buffers.h
> > > +++ b/libavcodec/v4l2_buffers.h
> > > @@ -55,6 +55,7 @@ typedef struct V4L2Buffer {  int bytesperline;
> > > void
> > > * mm_addr;  size_t length;
> > > +        int dmafd;
> > >  } plane_info[VIDEO_MAX_PLANES];
> > >
> > >  int num_planes;
> > > diff --git a/libavcodec/v4l2_context.c b/libavcodec/v4l2_context.c
> > > index b08f0015c2e5..f0406194293d 100644
> > > --- a/libavcodec/v4l2_context.c
> > > +++ b/libavcodec/v4l2_context.c
> > > @@ -453,6 +453,10 @@ static int v4l2_release_buffers(V4L2Context*
> > > ctx) if (p->mm_addr && p->length)  if (munmap(p->mm_addr, p->length)
> > > < 0) av_log(logger(ctx), AV_LOG_ERROR, "%s unmap plane (%s))\n",
> > > ctx->name, av_err2str(AVERROR(errno)));
> > > +            if (p->dmafd >= 0) {
> > > +                close(p->dmafd);
> > > +                p->dmafd = -1;
> > > +            }
> > >  }
> > >  }
> > >
> >
> > We already have a standard structure for representing DRM frames, it's
> > AV_PIX_FMT_DRM_PRIME, which encapsulates a AVDRMFrameDescriptor,
> which
> > contains DRM fds for every plane, and layer description.
> >
> > I think there may have been an old patch which did this, but I don't
> remember.
> 
> Thanks for your information, I'll check it
> 

Hi Lynne,
    Thank you again, I got the point, and then this patch can be dropped now.
    I'll try to export to AV_PIX_FMT_DRM_PRIME in v4l2 codec

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