[v1,09/17] docs: core-api: document the IOVA-based API

Commit Message

Leon Romanovsky Oct. 30, 2024, 3:12 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

Randy Dunlap Oct. 31, 2024, 1:41 a.m. UTC | #1

(nits)

On 10/30/24 8:12 AM, Leon Romanovsky wrote:
> 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(+)
> 
> diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dma-api.rst
> index 8e3cce3d0a23..6095696a65a7 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.

                    considerations

> +
> +::
> +
> +    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,
> +		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

                            previously

> +
> +::
> +
> +   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
>  --------------------------------------

Leon Romanovsky Oct. 31, 2024, 7:59 a.m. UTC | #2

On Wed, Oct 30, 2024 at 06:41:21PM -0700, Randy Dunlap wrote:
> (nits)
> 
> On 10/30/24 8:12 AM, Leon Romanovsky wrote:
> > 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(+)

<...>

> > +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.
> 
>                     considerations

<...>

> > +is used to unmap a range previous mapped, and
> 
>                             previously

Thanks

Patch

diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dma-api.rst
index 8e3cce3d0a23..6095696a65a7 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);
+
+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,
+		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
 --------------------------------------