On Wed, May 08, 2019 at 11:15:33AM +0200, Daniel Vetter wrote:
> On Tue, May 07, 2019 at 10:13:30AM +0200, Christian König wrote:
> > To allow a smooth transition from pinning buffer objects to dynamic
> > invalidation we first start to cache the sg_table for an attachment.
> >
> > Signed-off-by: Christian König <christian.koe...@amd.com>
> > ---
> > drivers/dma-buf/dma-buf.c | 24 ++++++++++++++++++++++++
> > include/linux/dma-buf.h | 14 ++++++++++++++
> > 2 files changed, 38 insertions(+)
> >
> > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> > index 7c858020d14b..775e13f54083 100644
> > --- a/drivers/dma-buf/dma-buf.c
> > +++ b/drivers/dma-buf/dma-buf.c
> > @@ -573,6 +573,20 @@ struct dma_buf_attachment *dma_buf_attach(struct
> > dma_buf *dmabuf,
> > list_add(&attach->node, &dmabuf->attachments);
> >
> > mutex_unlock(&dmabuf->lock);
> > +
> > + if (!dma_buf_is_dynamic(dmabuf)) {
> > + struct sg_table *sgt;
> > +
> > + sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL);
> > + if (!sgt)
> > + sgt = ERR_PTR(-ENOMEM);
> > + if (IS_ERR(sgt)) {
> > + dma_buf_detach(dmabuf, attach);
> > + return ERR_CAST(sgt);
> > + }
> > + attach->sgt = sgt;
> > + }
> > +
> > return attach;
> >
> > err_attach:
> > @@ -595,6 +609,10 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct
> > dma_buf_attachment *attach)
> > if (WARN_ON(!dmabuf || !attach))
> > return;
> >
> > + if (attach->sgt)
> > + dmabuf->ops->unmap_dma_buf(attach, attach->sgt,
> > + DMA_BIDIRECTIONAL);
> > +
> > mutex_lock(&dmabuf->lock);
> > list_del(&attach->node);
> > if (dmabuf->ops->detach)
> > @@ -630,6 +648,9 @@ struct sg_table *dma_buf_map_attachment(struct
> > dma_buf_attachment *attach,
> > if (WARN_ON(!attach || !attach->dmabuf))
> > return ERR_PTR(-EINVAL);
> >
> > + if (attach->sgt)
> > + return attach->sgt;
> > +
> > sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
> > if (!sg_table)
> > sg_table = ERR_PTR(-ENOMEM);
> > @@ -657,6 +678,9 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment
> > *attach,
> > if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
> > return;
> >
> > + if (attach->sgt == sg_table)
> > + return;
> > +
> > attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
> > direction);
> > }
> > diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> > index 58725f890b5b..52031fdc75bb 100644
> > --- a/include/linux/dma-buf.h
> > +++ b/include/linux/dma-buf.h
> > @@ -322,6 +322,7 @@ struct dma_buf_attachment {
> > struct dma_buf *dmabuf;
> > struct device *dev;
> > struct list_head node;
> > + struct sg_table *sgt;
> > void *priv;
> > };
> >
> > @@ -373,6 +374,19 @@ static inline void get_dma_buf(struct dma_buf *dmabuf)
> > get_file(dmabuf->file);
> > }
> >
> > +/**
> > + * dma_buf_is_dynamic - check if a DMA-buf uses dynamic mappings.
> > + * @dmabuf: the DMA-buf to check
> > + *
> > + * Returns true if a DMA-buf exporter wants to create dynamic sg table
> > mappings
> > + * for each attachment. False if only a single static sg table should be
> > used.
> > + */
> > +static inline bool dma_buf_is_dynamic(struct dma_buf *dmabuf)
> > +{
> > + /* Always use a static mapping for now */
> > + return false;
>
> Hm I still expect that later on we'll want this to be decided by the
> attachment: It's only dynamic if both the exporter and the importer
> support dynamic dma-buf management, otherwise we need to pin.
>
> But anyway, I feel like we need to go over the entire thing anyway once
> more when p2p has landed, on this:
>
> Reviewed-by: Daniel Vetter <daniel.vet...@ffwll.ch>
Correction that I only just realized, but need to retract that r-b on this
and the drm sgt cache removal patch: You now hardcode the direction to
DMA_BIDIRECTIONAL, drm_prime did only keep the cache for a given
direction.
Now x86 drivers always set DMA_BIDIRECTIONAL, but arm soc drivers (and
also v4l videobuf layer) try to guess whether it should be DMA_TO_DEVICE
or DMA_FROM_DEVICE. I have no idea what the implications are, also all the
cache coherency on dma-bufs is kinda ill-defined.
And we can't throw the sgt cache away at map time if it doesn't fit like
drm_prime does, because that reintroduces the reservation object lock,
defeating the entire purpose of this. Also we can't just assume drm_prime
works for everyone, since the special cases all roll their own dma-buf
import. I have also not checked what exactly exporters do. No idea what to
do here now.
/me cries
-Daniel
>
> > +}
> > +
> > struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> > struct device *dev);
> > void dma_buf_detach(struct dma_buf *dmabuf,
> > --
> > 2.17.1
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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