[PATCH] iommu: Improve the performance for direct_mapping

[Yong Wu]

Currently direct_mapping always use the smallest pgsize which is SZ_4K
normally to mapping. This is unnecessary. we could gather the size, and
call iommu_map then, iommu_map could decide how to map better with the
just right pgsize.

>From the original comment, we should take care overlap, otherwise,
iommu_map may return -EEXIST. In this overlap case, we should map the
previous region before overlap firstly. then map the left part.

Each a iommu device will call this direct_mapping when its iommu
initialize, This patch is effective to improve the boot/initialization
time especially while it only needs level 1 mapping.

Signed-off-by: Anan Sun <anan.sun@xxxxxxxxxxxx>
Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx>
---
 drivers/iommu/iommu.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index df87c8e825f7..854a8fcb928d 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -737,6 +737,7 @@ static int iommu_create_device_direct_mappings(struct iommu_group *group,
 	/* We need to consider overlapping regions for different devices */
 	list_for_each_entry(entry, &mappings, list) {
 		dma_addr_t start, end, addr;
+		size_t unmapped_sz = 0;
 
 		if (domain->ops->apply_resv_region)
 			domain->ops->apply_resv_region(dev, domain, entry);
@@ -752,10 +753,25 @@ static int iommu_create_device_direct_mappings(struct iommu_group *group,
 			phys_addr_t phys_addr;
 
 			phys_addr = iommu_iova_to_phys(domain, addr);
-			if (phys_addr)
+			if (phys_addr == 0) {
+				unmapped_sz += pg_size; /* Gather the size. */
 				continue;
+			}
 
-			ret = iommu_map(domain, addr, addr, pg_size, entry->prot);
+			if (unmapped_sz) {
+				/* Map the region before the overlap. */
+				ret = iommu_map(domain, start, start,
+						unmapped_sz, entry->prot);
+				if (ret)
+					goto out;
+				start += unmapped_sz;
+				unmapped_sz = 0;
+			}
+			start += pg_size;
+		}
+		if (unmapped_sz) {
+			ret = iommu_map(domain, start, start, unmapped_sz,
+					entry->prot);
 			if (ret)
 				goto out;
 		}
-- 
2.18.0