iommu: add kernel-doc for iommu_unmap_fast

Add kernel-doc section for iommu_unmap_fast to document existing
limitation of underlying functions which can't split individual ranges.

Suggested-by: Jason Gunthorpe <[email protected]>
Acked-by: Will Deacon <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Tested-by: Jens Axboe <[email protected]>
Reviewed-by: Jason Gunthorpe <[email protected]>
Reviewed-by: Luis Chamberlain <[email protected]>
Reviewed-by: Lu Baolu <[email protected]>
Signed-off-by: Leon Romanovsky <[email protected]>
Signed-off-by: Marek Szyprowski <[email protected]>

Author: rleon

drivers/iommu/iommu.c

@@ -2618,6 +2618,25 @@ size_t iommu_unmap(struct iommu_domain *domain,
 }
 EXPORT_SYMBOL_GPL(iommu_unmap);
 
+/**
+ * iommu_unmap_fast() - Remove mappings from a range of IOVA without IOTLB sync
+ * @domain: Domain to manipulate
+ * @iova: IO virtual address to start
+ * @size: Length of the range starting from @iova
+ * @iotlb_gather: range information for a pending IOTLB flush
+ *
+ * iommu_unmap_fast() will remove a translation created by iommu_map().
+ * It can't subdivide a mapping created by iommu_map(), so it should be
+ * called with IOVA ranges that match what was passed to iommu_map(). The
+ * range can aggregate contiguous iommu_map() calls so long as no individual
+ * range is split.
+ *
+ * Basically iommu_unmap_fast() is the same as iommu_unmap() but for callers
+ * which manage the IOTLB flushing externally to perform a batched sync.
+ *
+ * Returns: Number of bytes of IOVA unmapped. iova + res will be the point
+ * unmapping stopped.
+ */
 size_t iommu_unmap_fast(struct iommu_domain *domain,
 			unsigned long iova, size_t size,
 			struct iommu_iotlb_gather *iotlb_gather)