[PATCH v4 1/1] iommu-api: Add map_sg/unmap_sg functions

Any more comments on this from anyone before I submit v5?

On 8/1/2014 9:44 AM, Olav Haugan wrote:

Hi Will,

On 8/1/2014 1:22 AM, Will Deacon wrote:

quoted

Hi Olav,

On Fri, Aug 01, 2014 at 01:54:44AM +0100, Olav Haugan wrote:

quoted

Mapping and unmapping are more often than not in the critical path.
map_sg and unmap_sg allows IOMMU driver implementations to optimize
the process of mapping and unmapping buffers into the IOMMU page tables.

Instead of mapping a buffer one page at a time and requiring potentially
expensive TLB operations for each page, this function allows the driver
to map all pages in one go and defer TLB maintenance until after all
pages have been mapped.

Additionally, the mapping operation would be faster in general since
clients does not have to keep calling map API over and over again for
each physically contiguous chunk of memory that needs to be mapped to a
virtually contiguous region.

Just a couple of minor comments, but I think this is almost there now.

quoted

Signed-off-by: Olav Haugan <redacted>
---
 drivers/iommu/iommu.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 include/linux/iommu.h | 28 ++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 1698360..1d5dc2e 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c

@@ -1088,6 +1088,50 @@ size_t iommu_unmap(struct iommu_domain *domain, unsigned long iova, size_t size)
 }
 EXPORT_SYMBOL_GPL(iommu_unmap);
 
+int iommu_map_sg(struct iommu_domain *domain, unsigned long iova,
+			struct scatterlist *sg, unsigned int nents,
+			int prot, unsigned long flags)
+{

What do you anticipate passing in the flags parameter? I assume it's
something specific to the scatterlist, since we can't provide this to
iommu_map as it stands?

Initially the flags argument is planned to be used by clients to
indicate to the driver that no TLB operation is necessary. This allows
clients to for example map/unmap multiple scatter-gather lists without
doing expensive TLB invalidate operations for each call but just do this
at the last mapping/unmapping call instead. I believe Rob Clark was
looking for this feature and I can see the benefit for our use cases also.

quoted

quoted

+	int ret = 0;
+	unsigned long offset = 0;
+
+	if (unlikely(domain->ops->map_sg == NULL)) {
+		unsigned int i;
+		struct scatterlist *s;
+
+		for_each_sg(sg, s, nents, i) {
+			phys_addr_t phys = page_to_phys(sg_page(s));
+			size_t page_len = s->offset + s->length;
+
+			ret = iommu_map(domain, iova + offset, phys, page_len,
+					prot);
+			if (ret)
+				goto fail;
+
+			offset += page_len;
+		}
+	} else {
+		ret = domain->ops->map_sg(domain, iova, sg, nents, prot, flags);
+	}
+	goto out;
+
+fail:
+	/* undo mappings already done in case of error */
+	iommu_unmap(domain, iova, offset);

I think this would be cleaner if you stuck it in the loop above and removed
all these labels:

  if (ret) {
	iommu_unmap(...);
	break;
  }

Sure, I can do that.

Thanks,

Olav

Olav

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