Re: [PATCH 03/12] dma-buf: start caching of sg_table objects

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Apr 26, 2019 at 02:36:29PM +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
> unless the driver has implemented the explicite pin/unpin callbacks.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>

Correction on my "squash everything" suggestion: I think this patch here
still needs to be separate, so that "why did this cause a regression" is
easier to understand. But with a small nit.

> ---
>  drivers/dma-buf/dma-buf.c | 24 ++++++++++++++++++++++++
>  include/linux/dma-buf.h   |  1 +
>  2 files changed, 25 insertions(+)
> 
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 0656dcf289be..a18d10c4425a 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -610,6 +610,20 @@ dma_buf_attach(const struct dma_buf_attach_info *info)
>  	list_add(&attach->node, &dmabuf->attachments);
>  
>  	mutex_unlock(&dmabuf->lock);
> +
> +	if (!dmabuf->ops->pin) {

I think a static inline dma_buf_is_dynamic_attachment() would be good
here, which in this patch (since it's ealier) would always return false.

Aside: I think only checking pin here (i.e. can the exporter do dynamic
mappings) isn't good enough, we also need to check for the importers
->invalidate. Hence _is_dynamic_attachment, not _is_dynamic_dma_buf. If we
don't also check for the importer we again have a reservation lock in
dma_buf_map/unmap, which we know will anger the lockdep gods ...
-Daniel

> +		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:
> @@ -632,6 +646,10 @@ 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)
> @@ -668,6 +686,9 @@ 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;
> +
>  	reservation_object_lock(attach->dmabuf->resv, NULL);
>  	r = dma_buf_pin(attach->dmabuf);
>  	reservation_object_unlock(attach->dmabuf->resv);
> @@ -701,6 +722,9 @@ 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 0321939b1c3d..b9d0719581cd 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -345,6 +345,7 @@ struct dma_buf_attachment {
>  	struct dma_buf *dmabuf;
>  	struct device *dev;
>  	struct list_head node;
> +	struct sg_table *sgt;
>  	void *priv;
>  };
>  
> -- 
> 2.17.1
> 
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> dri-devel@lists.freedesktop.org
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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