[09/18] docs: core-api: document the IOVA-based API

Commit Message

Leon Romanovsky Oct. 27, 2024, 2:21 p.m. UTC

From: Christoph Hellwig <[e-mail]>

Add an explanation of the newly added IOVA-based mapping API.

Signed-off-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Leon Romanovsky <[e-mail]>
---
 Documentation/core-api/dma-api.rst | 70 ++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)

Comments

Logan Gunthorpe Oct. 28, 2024, 6:12 p.m. UTC | #1

I noticed a couple of typos below:

On 2024-10-27 08:21, Leon Romanovsky wrote:

> +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

The second 'dma' should be capitalized as it is in other uses.


> +    int dma_iova_sync(struct device *dev, struct dma_iova_state *state,
> +		size_t offset, size_t size, int ret);
> +
> +Must called to sync the IOMMU page tables for IOVA-range mapped by one or
> +more calls to ``dma_iova_link()``.

"Must be called" instead of "Must called"

Thanks,

Logan

Leon Romanovsky Oct. 28, 2024, 6:28 p.m. UTC | #2

On Mon, Oct 28, 2024 at 12:12:34PM -0600, Logan Gunthorpe wrote:
> 
> I noticed a couple of typos below:
> 
> On 2024-10-27 08:21, Leon Romanovsky wrote:
> 
> > +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
> 
> The second 'dma' should be capitalized as it is in other uses.
> 
> 
> > +    int dma_iova_sync(struct device *dev, struct dma_iova_state *state,
> > +		size_t offset, size_t size, int ret);
> > +
> > +Must called to sync the IOMMU page tables for IOVA-range mapped by one or
> > +more calls to ``dma_iova_link()``.
> 
> "Must be called" instead of "Must called"

Thanks, will fix.

> 
> Thanks,
> 
> Logan

Patch

diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dma-api.rst
index 8e3cce3d0a23..9ecbff473d9a 100644
--- a/Documentation/core-api/dma-api.rst
+++ b/Documentation/core-api/dma-api.rst
@@ -530,6 +530,76 @@  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 consideration 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, int ret);
+
+Must 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,
+		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 previous 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
 --------------------------------------