Merge tag 'dma-mapping-6.16-2025-05-26' of git://git.kernel.org/pub/scm/linux/kernel/git/mszyprowski/linux

Pull dma-mapping updates from Marek Szyprowski:
 "New two step DMA mapping API, which is is a first step to a long path
  to provide alternatives to scatterlist and to remove hacks, abuses and
  design mistakes related to scatterlists.

  This new approach optimizes some calls to DMA-IOMMU layer and cache
  maintenance by batching them, reduces memory usage as it is no need to
  store mapped DMA addresses to unmap them, and reduces some function
  call overhead.  It is a combination effort of many people, lead and
  developed by Christoph Hellwig and Leon Romanovsky"

* tag 'dma-mapping-6.16-2025-05-26' of git://git.kernel.org/pub/scm/linux/kernel/git/mszyprowski/linux:
  docs: core-api: document the IOVA-based API
  dma-mapping: add a dma_need_unmap helper
  dma-mapping: Implement link/unlink ranges API
  iommu/dma: Factor out a iommu_dma_map_swiotlb helper
  dma-mapping: Provide an interface to allow allocate IOVA
  iommu: add kernel-doc for iommu_unmap_fast
  iommu: generalize the batched sync after map interface
  dma-mapping: move the PCI P2PDMA mapping helpers to pci-p2pdma.h
  PCI/P2PDMA: Refactor the p2pdma mapping helpers

1 files changed, 71 insertions, 0 deletions

diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dma-api.rst
index 8e3cce3d0a23..2ad08517e626 100644
--- a/Documentation/core-api/dma-api.rst
+++ b/Documentation/core-api/dma-api.rst
@@ -530,6 +530,77 @@ routines, e.g.:::
 		....
 	}
 
+Part Ie - IOVA-based DMA mappings
+---------------------------------
+
+These APIs allow a very efficient mapping when using an IOMMU.  They are an
+optional path that requires extra code and are only recommended for drivers
+where DMA mapping performance, or the space usage for storing the DMA addresses
+matter.  All the considerations from the previous section apply here as well.
+
+::
+
+    bool dma_iova_try_alloc(struct device *dev, struct dma_iova_state *state,
+		phys_addr_t phys, size_t size);
+
+Is used to try to allocate IOVA space for mapping operation.  If it returns
+false this API can't be used for the given device and the normal streaming
+DMA mapping API should be used.  The ``struct dma_iova_state`` is allocated
+by the driver and must be kept around until unmap time.
+
+::
+
+    static inline bool dma_use_iova(struct dma_iova_state *state)
+
+Can be used by the driver to check if the IOVA-based API is used after a
+call to dma_iova_try_alloc.  This can be useful in the unmap path.
+
+::
+
+    int dma_iova_link(struct device *dev, struct dma_iova_state *state,
+		phys_addr_t phys, size_t offset, size_t size,
+		enum dma_data_direction dir, unsigned long attrs);
+
+Is used to link ranges to the IOVA previously allocated.  The start of all
+but the first call to dma_iova_link for a given state must be aligned
+to the DMA merge boundary returned by ``dma_get_merge_boundary())``, and
+the size of all but the last range must be aligned to the DMA merge boundary
+as well.
+
+::
+
+    int dma_iova_sync(struct device *dev, struct dma_iova_state *state,
+		size_t offset, size_t size);
+
+Must be called to sync the IOMMU page tables for IOVA-range mapped by one or
+more calls to ``dma_iova_link()``.
+
+For drivers that use a one-shot mapping, all ranges can be unmapped and the
+IOVA freed by calling:
+
+::
+
+   void dma_iova_destroy(struct device *dev, struct dma_iova_state *state,
+		size_t mapped_len, enum dma_data_direction dir,
+                unsigned long attrs);
+
+Alternatively drivers can dynamically manage the IOVA space by unmapping
+and mapping individual regions.  In that case
+
+::
+
+    void dma_iova_unlink(struct device *dev, struct dma_iova_state *state,
+		size_t offset, size_t size, enum dma_data_direction dir,
+		unsigned long attrs);
+
+is used to unmap a range previously mapped, and
+
+::
+
+   void dma_iova_free(struct device *dev, struct dma_iova_state *state);
+
+is used to free the IOVA space.  All regions must have been unmapped using
+``dma_iova_unlink()`` before calling ``dma_iova_free()``.
 
 Part II - Non-coherent DMA allocations
 --------------------------------------