Re: [PATCH 1/2] dma-buf: start caching of sg_table objects v2

[Christian König <ckoenig.leichtzumerken@xxxxxxxxx>]

Am 15.05.19 um 10:58 schrieb Daniel Vetter:
> On Tue, May 14, 2019 at 04:05:14PM +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.
> >
> > v2: keep closer to the DRM implementation
> >
> > Signed-off-by: Christian König <christian.koenig@xxxxxxx>
> i915 doesn't use the prime helpers, so this would be a change for us.

Not a problem at all, see below. I've added an cache_sgt_mapping member 
into the dma_buf_ops structure. Only when this member is true the 
functionality is enabled.

So I'm just moving code around in those two patches and no functional 
change at all.

Regards,
Christian.

>   Not
> sure that matters. Since we can't use this as an easy way out of the
> locking problem around reservation_object I'm not sure how useful it is to
> move this ahead. At least until we have a clearer picture on how we plan
> to roll out the dynamic dma-buf stuff. Once we have a bit more clarity
> there I'm all for merging prep work, but as-is I'd be cautious ... This
> stuff is a lot more tricky than it seems at first :-/
> -Daniel
> > ---
> >   drivers/dma-buf/dma-buf.c | 27 +++++++++++++++++++++++++--
> >   include/linux/dma-buf.h   | 13 +++++++++++++
> >   2 files changed, 38 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> > index 7c858020d14b..a2d34c6b80a5 100644
> > --- a/drivers/dma-buf/dma-buf.c
> > +++ b/drivers/dma-buf/dma-buf.c
> > @@ -573,6 +573,7 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> >   	list_add(&attach->node, &dmabuf->attachments);
> >   
> >   	mutex_unlock(&dmabuf->lock);
> > +
> >   	return attach;
> >   
> >   err_attach:
> > @@ -595,6 +596,9 @@ 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, attach->dir);
> > +
> >   	mutex_lock(&dmabuf->lock);
> >   	list_del(&attach->node);
> >   	if (dmabuf->ops->detach)
> > @@ -630,10 +634,27 @@ 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) {
> > +		/*
> > +		 * Two mappings with different directions for the same
> > +		 * attachment are not allowed.
> > +		 */
> > +		if (attach->dir != direction &&
> > +		    attach->dir != DMA_BIDIRECTIONAL)
> > +			return ERR_PTR(-EBUSY);
> > +
> > +		return attach->sgt;
> > +	}
> > +
> >   	sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
> >   	if (!sg_table)
> >   		sg_table = ERR_PTR(-ENOMEM);
> >   
> > +	if (!IS_ERR(sg_table) && attach->dmabuf->ops->cache_sgt_mapping) {
> > +		attach->sgt = sg_table;
> > +		attach->dir = direction;
> > +	}
> > +
> >   	return sg_table;
> >   }
> >   EXPORT_SYMBOL_GPL(dma_buf_map_attachment);
> > @@ -657,8 +678,10 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
> >   	if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
> >   		return;
> >   
> > -	attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
> > -						direction);
> > +	if (attach->sgt == sg_table)
> > +		return;
> > +
> > +	attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
> >   }
> >   EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
> >   
> > diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> > index 58725f890b5b..45b9767e67ec 100644
> > --- a/include/linux/dma-buf.h
> > +++ b/include/linux/dma-buf.h
> > @@ -51,6 +51,15 @@ struct dma_buf_attachment;
> >    * @vunmap: [optional] unmaps a vmap from the buffer
> >    */
> >   struct dma_buf_ops {
> > +	/**
> > +	  * @cache_sgt_mapping:
> > +	  *
> > +	  * If true the framework will cache the first mapping made for each
> > +	  * attachment. This avoids creating mappings for attachments multiple
> > +	  * times.
> > +	  */
> > +	bool cache_sgt_mapping;
> > +
> >   	/**
> >   	 * @attach:
> >   	 *
> > @@ -307,6 +316,8 @@ struct dma_buf {
> >    * @dmabuf: buffer for this attachment.
> >    * @dev: device attached to the buffer.
> >    * @node: list of dma_buf_attachment.
> > + * @sgt: cached mapping.
> > + * @dir: direction of cached mapping.
> >    * @priv: exporter specific attachment data.
> >    *
> >    * This structure holds the attachment information between the dma_buf buffer
> > @@ -322,6 +333,8 @@ struct dma_buf_attachment {
> >   	struct dma_buf *dmabuf;
> >   	struct device *dev;
> >   	struct list_head node;
> > +	struct sg_table *sgt;
> > +	enum dma_data_direction dir;
> >   	void *priv;
> >   };
> >   
> > --
> > 2.17.1

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