Re: [PATCH 1/9] dma-buf: start caching of sg_table objects

[Daniel Vetter <daniel@ffwll.ch>]

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.koenig@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.vetter@ffwll.ch>

> +}
> +
>  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
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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