Hi Tomasz,
Thanks for the review!
On Tue, Apr 2, 2024 at 7:21 PM Tomasz Figa <tfiga@xxxxxxxxxxxx> wrote:
>
> Hi Yunke,
>
> On Mon, Apr 1, 2024 at 3:35 PM Yunke Cao <yunkec@xxxxxxxxxxxx> wrote:
> >
> > When multiple planes use the same dma buf, each plane will have its own dma
> > buf attachment and mapping. It is a waste of IOVA space.
> >
> > This patch adds a duplicated_dbuf flag in vb2_plane. If a plane's dbuf
> > is the same as an existing plane, do not create another attachment and
> > mapping.
> >
> > Signed-off-by: Yunke Cao <yunkec@xxxxxxxxxxxx>
> > ---
> > .../media/common/videobuf2/videobuf2-core.c | 30 +++++++++++++++----
> > include/media/videobuf2-core.h | 3 ++
> > 2 files changed, 28 insertions(+), 5 deletions(-)
> >
>
> Thanks a lot for the patch! Please take a look at my comments inline.
>
> > diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> > index b6bf8f232f48..b03e058ef2b1 100644
> > --- a/drivers/media/common/videobuf2/videobuf2-core.c
> > +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> > @@ -304,10 +304,13 @@ static void __vb2_plane_dmabuf_put(struct vb2_buffer *vb, struct vb2_plane *p)
> > if (!p->mem_priv)
> > return;
> >
> > - if (p->dbuf_mapped)
> > - call_void_memop(vb, unmap_dmabuf, p->mem_priv);
> > + if (!p->duplicated_dbuf) {
> > + if (p->dbuf_mapped)
> > + call_void_memop(vb, unmap_dmabuf, p->mem_priv);
> > +
> > + call_void_memop(vb, detach_dmabuf, p->mem_priv);
>
> I wonder if we may want to reverse the iteration order in
> __vb2_buf_dmabuf_put() so that we don't leave dangling pointers in
> further planes when previous planes have their mem_priv freed.
>
The loop in __prepare_dmabuf() is of the same iteration order, so the
same will happen.
Is it still necessary to reverse the order in __vb2_buf_dmabuf_put()?
> > + }
> >
> > - call_void_memop(vb, detach_dmabuf, p->mem_priv);
> > dma_buf_put(p->dbuf);
> > p->mem_priv = NULL;
> > p->dbuf = NULL;
> > @@ -1327,7 +1330,7 @@ static int __prepare_dmabuf(struct vb2_buffer *vb)
> > struct vb2_plane planes[VB2_MAX_PLANES];
> > struct vb2_queue *q = vb->vb2_queue;
> > void *mem_priv;
> > - unsigned int plane;
> > + unsigned int plane, i;
> > int ret = 0;
> > bool reacquired = vb->planes[0].mem_priv == NULL;
> >
> > @@ -1383,6 +1386,22 @@ static int __prepare_dmabuf(struct vb2_buffer *vb)
> > vb->planes[plane].m.fd = 0;
> > vb->planes[plane].data_offset = 0;
> >
> > + if (mem_priv && plane > 0) {
>
> Is mem_priv the right thing to check for here? I think it would point
> to the private data of the previous plane (i.e. plane - 1), but in the
> loop below we may end up finding the match in an earlier plane (e.g.
> plane - 2).
>
> > + for (i = 0; i < plane; ++i) {
> > + if (dbuf == vb->planes[i].dbuf) {
> > + vb->planes[plane].duplicated_dbuf = true;
>
> I guess we can set ...[plane].mem_priv to [i].mem_priv here.
>
> > + break;
> > + }
> > + }
> > + }
> > +
> > + /* There's no need to attach a duplicated dbuf. */
> > + if (vb->planes[plane].duplicated_dbuf) {
> > + vb->planes[plane].dbuf = dbuf;
> > + vb->planes[plane].mem_priv = mem_priv;
>
> I think this mem_priv would be the one from planes[plane-1] and not
> necessarily the one with matching dbuf.
Thanks for catching the error. Will fix it in the next version.
>
>
> > + continue;
> > + }
> > +
> > /* Acquire each plane's memory */
> > mem_priv = call_ptr_memop(attach_dmabuf,
> > vb,
> > @@ -1396,6 +1415,7 @@ static int __prepare_dmabuf(struct vb2_buffer *vb)
> > goto err;
> > }
> >
> > + vb->planes[plane].duplicated_dbuf = false;
> > vb->planes[plane].dbuf = dbuf;
> > vb->planes[plane].mem_priv = mem_priv;
> > }
> > @@ -1406,7 +1426,7 @@ static int __prepare_dmabuf(struct vb2_buffer *vb)
> > * userspace knows sooner rather than later if the dma-buf map fails.
> > */
> > for (plane = 0; plane < vb->num_planes; ++plane) {
> > - if (vb->planes[plane].dbuf_mapped)
> > + if (vb->planes[plane].dbuf_mapped || vb->planes[plane].duplicated_dbuf)
> > continue;
> >
> > ret = call_memop(vb, map_dmabuf, vb->planes[plane].mem_priv);
> > diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> > index 8b86996b2719..5db781da2ebc 100644
> > --- a/include/media/videobuf2-core.h
> > +++ b/include/media/videobuf2-core.h
> > @@ -154,6 +154,8 @@ struct vb2_mem_ops {
> > * @mem_priv: private data with this plane.
> > * @dbuf: dma_buf - shared buffer object.
> > * @dbuf_mapped: flag to show whether dbuf is mapped or not
> > + * @duplicated_dbuf: boolean to show whether dbuf is duplicated with a
> > + * previous plane of the buffer.
> > * @bytesused: number of bytes occupied by data in the plane (payload).
> > * @length: size of this plane (NOT the payload) in bytes. The maximum
> > * valid size is MAX_UINT - PAGE_SIZE.
> > @@ -179,6 +181,7 @@ struct vb2_plane {
> > void *mem_priv;
> > struct dma_buf *dbuf;
> > unsigned int dbuf_mapped;
> > + bool duplicated_dbuf;
>
> nit: We kind of seem to use the dbuf_ prefix already, so how about
> dbuf_duplicated? Or maybe dbuf_reused? Hmm, naming is always hard...
>
dbuf_duplicated sounds good to me.
Best,
Yunke
> Best regards,
> Tomasz
