iommu: add iommu_device_max_index IOMMU helper function

This function helps IOMMUs to know the highest address that a device
can access to.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/iommu-helper.h b/include/linux/iommu-helper.h
index c975caf75385..58f41107e4ae 100644
--- a/include/linux/iommu-helper.h
+++ b/include/linux/iommu-helper.h
@@ -1,3 +1,13 @@
+static inline unsigned long iommu_device_max_index(unsigned long size,
+                                                   unsigned long offset,
+                                                   u64 dma_mask)
+{
+        if (size + offset > dma_mask)
+                return dma_mask - offset + 1;
+        else
+                return size;
+}
+
 extern int iommu_is_span_boundary(unsigned int index, unsigned int nr,
                                   unsigned long shift,
                                   unsigned long boundary_size);