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

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Am 08.05.19 um 11:15 schrieb Daniel Vetter:
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@xxxxxxx>
---
  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.

Yeah, essentially we need to handle the following cases:

1. Static DMA-buf and the exporter doesn't want caching.
2. Static DMA-buf and the exporter does want caching.
3. Dynamic DMA-buf and we use caching as a workaround for smooth transition.
4. Dynamic DMA-buf and caching doesn't make much sense.

So far we only support 3 & 4 and not 1 & 2. Could be that this gets much more complicated, but I would only want to add this complicated code if we really find that we need it.

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@xxxxxxxx>

Thanks for the review, next question how do we merge this? Through drm-misc?

Regards,
Christian.


+}
+
  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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