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.

Signed-off-by: Olav Haugan <redacted>
---
 drivers/iommu/iommu.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/iommu.h | 28 ++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 1698360..cd65511 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c

@@ -1088,6 +1088,54 @@ 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)
+{
+	int ret = 0;
+	unsigned long offset = 0;
+
+	BUG_ON(iova & (~PAGE_MASK));
+
+	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));
+			u32 page_len = PAGE_ALIGN(s->offset + s->length);