diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/core-api/dma-api.rst | 49 |
1 files changed, 43 insertions, 6 deletions
diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dma-api.rst index ea0413276ddb..75cb757bbff0 100644 --- a/Documentation/core-api/dma-api.rst +++ b/Documentation/core-api/dma-api.rst @@ -519,10 +519,9 @@ routines, e.g.::: Part II - Non-coherent DMA allocations -------------------------------------- -These APIs allow to allocate pages in the kernel direct mapping that are -guaranteed to be DMA addressable. This means that unlike dma_alloc_coherent, -virt_to_page can be called on the resulting address, and the resulting -struct page can be used for everything a struct page is suitable for. +These APIs allow to allocate pages that are guaranteed to be DMA addressable +by the passed in device, but which need explicit management of memory ownership +for the kernel vs the device. If you don't understand how cache line coherency works between a processor and an I/O device, you should not be using this part of the API. @@ -537,7 +536,7 @@ an I/O device, you should not be using this part of the API. This routine allocates a region of <size> bytes of consistent memory. It returns a pointer to the allocated region (in the processor's virtual address space) or NULL if the allocation failed. The returned memory may or may not -be in the kernels direct mapping. Drivers must not call virt_to_page on +be in the kernel direct mapping. Drivers must not call virt_to_page on the returned memory region. It also returns a <dma_handle> which may be cast to an unsigned integer the @@ -565,7 +564,45 @@ reused. Free a region of memory previously allocated using dma_alloc_noncoherent(). dev, size and dma_handle and dir must all be the same as those passed into dma_alloc_noncoherent(). cpu_addr must be the virtual address returned by -the dma_alloc_noncoherent(). +dma_alloc_noncoherent(). + +:: + + struct page * + dma_alloc_pages(struct device *dev, size_t size, dma_addr_t *dma_handle, + enum dma_data_direction dir, gfp_t gfp) + +This routine allocates a region of <size> bytes of non-coherent memory. It +returns a pointer to first struct page for the region, or NULL if the +allocation failed. The resulting struct page can be used for everything a +struct page is suitable for. + +It also returns a <dma_handle> which may be cast to an unsigned integer the +same width as the bus and given to the device as the DMA address base of +the region. + +The dir parameter specified if data is read and/or written by the device, +see dma_map_single() for details. + +The gfp parameter allows the caller to specify the ``GFP_`` flags (see +kmalloc()) for the allocation, but rejects flags used to specify a memory +zone such as GFP_DMA or GFP_HIGHMEM. + +Before giving the memory to the device, dma_sync_single_for_device() needs +to be called, and before reading memory written by the device, +dma_sync_single_for_cpu(), just like for streaming DMA mappings that are +reused. + +:: + + void + dma_free_pages(struct device *dev, size_t size, struct page *page, + dma_addr_t dma_handle, enum dma_data_direction dir) + +Free a region of memory previously allocated using dma_alloc_pages(). +dev, size and dma_handle and dir must all be the same as those passed into +dma_alloc_noncoherent(). page must be the pointer returned by +dma_alloc_pages(). :: |