iommu: add kernel-doc for iommu_unmap_fast

JIRA: https://issues.redhat.com/browse/RHEL-113839
Upstream-Status: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

commit dc2e692
Author: Leon Romanovsky <leonro@nvidia.com>
Date:   Mon May 5 10:01:41 2025 +0300

    iommu: add kernel-doc for iommu_unmap_fast

    Add missing kernel-doc comment for iommu_unmap_fast() function.

    Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
    Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

(cherry picked from commit dc2e692)
Co-developed-by: Claude claude-sonnet-4
Signed-off-by: Jerry Snitselaar <jsnitsel@redhat.com>

Author: snits

drivers/iommu/iommu.c

@@ -2587,6 +2587,25 @@ 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)