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832 lines
30 KiB
832 lines
30 KiB
============================================ |
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Dynamic DMA mapping using the generic device |
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============================================ |
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:Author: James E.J. Bottomley <[email protected]> |
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This document describes the DMA API. For a more gentle introduction |
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of the API (and actual examples), see Documentation/core-api/dma-api-howto.rst. |
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This API is split into two pieces. Part I describes the basic API. |
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Part II describes extensions for supporting non-consistent memory |
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machines. Unless you know that your driver absolutely has to support |
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non-consistent platforms (this is usually only legacy platforms) you |
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should only use the API described in part I. |
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Part I - dma_API |
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---------------- |
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To get the dma_API, you must #include <linux/dma-mapping.h>. This |
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provides dma_addr_t and the interfaces described below. |
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A dma_addr_t can hold any valid DMA address for the platform. It can be |
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given to a device to use as a DMA source or target. A CPU cannot reference |
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a dma_addr_t directly because there may be translation between its physical |
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address space and the DMA address space. |
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Part Ia - Using large DMA-coherent buffers |
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------------------------------------------ |
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:: |
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void * |
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dma_alloc_coherent(struct device *dev, size_t size, |
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dma_addr_t *dma_handle, gfp_t flag) |
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Consistent memory is memory for which a write by either the device or |
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the processor can immediately be read by the processor or device |
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without having to worry about caching effects. (You may however need |
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to make sure to flush the processor's write buffers before telling |
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devices to read that memory.) |
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This routine allocates a region of <size> bytes of consistent memory. |
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It returns a pointer to the allocated region (in the processor's virtual |
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address space) or NULL if the allocation failed. |
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It also returns a <dma_handle> which may be cast to an unsigned integer the |
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same width as the bus and given to the device as the DMA address base of |
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the region. |
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Note: consistent memory can be expensive on some platforms, and the |
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minimum allocation length may be as big as a page, so you should |
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consolidate your requests for consistent memory as much as possible. |
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The simplest way to do that is to use the dma_pool calls (see below). |
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The flag parameter (dma_alloc_coherent() only) allows the caller to |
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specify the ``GFP_`` flags (see kmalloc()) for the allocation (the |
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implementation may choose to ignore flags that affect the location of |
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the returned memory, like GFP_DMA). |
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:: |
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void |
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dma_free_coherent(struct device *dev, size_t size, void *cpu_addr, |
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dma_addr_t dma_handle) |
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Free a region of consistent memory you previously allocated. dev, |
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size and dma_handle must all be the same as those passed into |
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dma_alloc_coherent(). cpu_addr must be the virtual address returned by |
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the dma_alloc_coherent(). |
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Note that unlike their sibling allocation calls, these routines |
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may only be called with IRQs enabled. |
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Part Ib - Using small DMA-coherent buffers |
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------------------------------------------ |
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To get this part of the dma_API, you must #include <linux/dmapool.h> |
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Many drivers need lots of small DMA-coherent memory regions for DMA |
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descriptors or I/O buffers. Rather than allocating in units of a page |
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or more using dma_alloc_coherent(), you can use DMA pools. These work |
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much like a struct kmem_cache, except that they use the DMA-coherent allocator, |
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not __get_free_pages(). Also, they understand common hardware constraints |
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for alignment, like queue heads needing to be aligned on N-byte boundaries. |
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:: |
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struct dma_pool * |
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dma_pool_create(const char *name, struct device *dev, |
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size_t size, size_t align, size_t alloc); |
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dma_pool_create() initializes a pool of DMA-coherent buffers |
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for use with a given device. It must be called in a context which |
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can sleep. |
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The "name" is for diagnostics (like a struct kmem_cache name); dev and size |
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are like what you'd pass to dma_alloc_coherent(). The device's hardware |
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alignment requirement for this type of data is "align" (which is expressed |
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in bytes, and must be a power of two). If your device has no boundary |
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crossing restrictions, pass 0 for alloc; passing 4096 says memory allocated |
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from this pool must not cross 4KByte boundaries. |
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:: |
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void * |
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dma_pool_zalloc(struct dma_pool *pool, gfp_t mem_flags, |
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dma_addr_t *handle) |
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Wraps dma_pool_alloc() and also zeroes the returned memory if the |
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allocation attempt succeeded. |
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:: |
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void * |
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dma_pool_alloc(struct dma_pool *pool, gfp_t gfp_flags, |
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dma_addr_t *dma_handle); |
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This allocates memory from the pool; the returned memory will meet the |
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size and alignment requirements specified at creation time. Pass |
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GFP_ATOMIC to prevent blocking, or if it's permitted (not |
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in_interrupt, not holding SMP locks), pass GFP_KERNEL to allow |
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blocking. Like dma_alloc_coherent(), this returns two values: an |
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address usable by the CPU, and the DMA address usable by the pool's |
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device. |
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:: |
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void |
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dma_pool_free(struct dma_pool *pool, void *vaddr, |
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dma_addr_t addr); |
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This puts memory back into the pool. The pool is what was passed to |
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dma_pool_alloc(); the CPU (vaddr) and DMA addresses are what |
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were returned when that routine allocated the memory being freed. |
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:: |
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void |
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dma_pool_destroy(struct dma_pool *pool); |
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dma_pool_destroy() frees the resources of the pool. It must be |
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called in a context which can sleep. Make sure you've freed all allocated |
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memory back to the pool before you destroy it. |
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Part Ic - DMA addressing limitations |
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------------------------------------ |
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:: |
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int |
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dma_set_mask_and_coherent(struct device *dev, u64 mask) |
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Checks to see if the mask is possible and updates the device |
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streaming and coherent DMA mask parameters if it is. |
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Returns: 0 if successful and a negative error if not. |
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:: |
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int |
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dma_set_mask(struct device *dev, u64 mask) |
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Checks to see if the mask is possible and updates the device |
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parameters if it is. |
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Returns: 0 if successful and a negative error if not. |
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:: |
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int |
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dma_set_coherent_mask(struct device *dev, u64 mask) |
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Checks to see if the mask is possible and updates the device |
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parameters if it is. |
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Returns: 0 if successful and a negative error if not. |
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:: |
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u64 |
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dma_get_required_mask(struct device *dev) |
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This API returns the mask that the platform requires to |
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operate efficiently. Usually this means the returned mask |
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is the minimum required to cover all of memory. Examining the |
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required mask gives drivers with variable descriptor sizes the |
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opportunity to use smaller descriptors as necessary. |
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Requesting the required mask does not alter the current mask. If you |
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wish to take advantage of it, you should issue a dma_set_mask() |
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call to set the mask to the value returned. |
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:: |
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size_t |
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dma_max_mapping_size(struct device *dev); |
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Returns the maximum size of a mapping for the device. The size parameter |
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of the mapping functions like dma_map_single(), dma_map_page() and |
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others should not be larger than the returned value. |
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:: |
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bool |
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dma_need_sync(struct device *dev, dma_addr_t dma_addr); |
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Returns %true if dma_sync_single_for_{device,cpu} calls are required to |
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transfer memory ownership. Returns %false if those calls can be skipped. |
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:: |
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unsigned long |
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dma_get_merge_boundary(struct device *dev); |
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Returns the DMA merge boundary. If the device cannot merge any the DMA address |
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segments, the function returns 0. |
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Part Id - Streaming DMA mappings |
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-------------------------------- |
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:: |
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dma_addr_t |
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dma_map_single(struct device *dev, void *cpu_addr, size_t size, |
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enum dma_data_direction direction) |
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Maps a piece of processor virtual memory so it can be accessed by the |
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device and returns the DMA address of the memory. |
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The direction for both APIs may be converted freely by casting. |
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However the dma_API uses a strongly typed enumerator for its |
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direction: |
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======================= ============================================= |
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DMA_NONE no direction (used for debugging) |
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DMA_TO_DEVICE data is going from the memory to the device |
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DMA_FROM_DEVICE data is coming from the device to the memory |
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DMA_BIDIRECTIONAL direction isn't known |
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======================= ============================================= |
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.. note:: |
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Not all memory regions in a machine can be mapped by this API. |
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Further, contiguous kernel virtual space may not be contiguous as |
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physical memory. Since this API does not provide any scatter/gather |
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capability, it will fail if the user tries to map a non-physically |
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contiguous piece of memory. For this reason, memory to be mapped by |
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this API should be obtained from sources which guarantee it to be |
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physically contiguous (like kmalloc). |
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Further, the DMA address of the memory must be within the |
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dma_mask of the device (the dma_mask is a bit mask of the |
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addressable region for the device, i.e., if the DMA address of |
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the memory ANDed with the dma_mask is still equal to the DMA |
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address, then the device can perform DMA to the memory). To |
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ensure that the memory allocated by kmalloc is within the dma_mask, |
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the driver may specify various platform-dependent flags to restrict |
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the DMA address range of the allocation (e.g., on x86, GFP_DMA |
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guarantees to be within the first 16MB of available DMA addresses, |
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as required by ISA devices). |
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Note also that the above constraints on physical contiguity and |
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dma_mask may not apply if the platform has an IOMMU (a device which |
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maps an I/O DMA address to a physical memory address). However, to be |
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portable, device driver writers may *not* assume that such an IOMMU |
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exists. |
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.. warning:: |
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Memory coherency operates at a granularity called the cache |
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line width. In order for memory mapped by this API to operate |
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correctly, the mapped region must begin exactly on a cache line |
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boundary and end exactly on one (to prevent two separately mapped |
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regions from sharing a single cache line). Since the cache line size |
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may not be known at compile time, the API will not enforce this |
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requirement. Therefore, it is recommended that driver writers who |
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don't take special care to determine the cache line size at run time |
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only map virtual regions that begin and end on page boundaries (which |
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are guaranteed also to be cache line boundaries). |
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DMA_TO_DEVICE synchronisation must be done after the last modification |
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of the memory region by the software and before it is handed off to |
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the device. Once this primitive is used, memory covered by this |
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primitive should be treated as read-only by the device. If the device |
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may write to it at any point, it should be DMA_BIDIRECTIONAL (see |
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below). |
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DMA_FROM_DEVICE synchronisation must be done before the driver |
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accesses data that may be changed by the device. This memory should |
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be treated as read-only by the driver. If the driver needs to write |
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to it at any point, it should be DMA_BIDIRECTIONAL (see below). |
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DMA_BIDIRECTIONAL requires special handling: it means that the driver |
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isn't sure if the memory was modified before being handed off to the |
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device and also isn't sure if the device will also modify it. Thus, |
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you must always sync bidirectional memory twice: once before the |
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memory is handed off to the device (to make sure all memory changes |
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are flushed from the processor) and once before the data may be |
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accessed after being used by the device (to make sure any processor |
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cache lines are updated with data that the device may have changed). |
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:: |
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void |
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dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size, |
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enum dma_data_direction direction) |
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Unmaps the region previously mapped. All the parameters passed in |
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must be identical to those passed in (and returned) by the mapping |
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API. |
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:: |
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dma_addr_t |
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dma_map_page(struct device *dev, struct page *page, |
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unsigned long offset, size_t size, |
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enum dma_data_direction direction) |
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void |
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dma_unmap_page(struct device *dev, dma_addr_t dma_address, size_t size, |
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enum dma_data_direction direction) |
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API for mapping and unmapping for pages. All the notes and warnings |
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for the other mapping APIs apply here. Also, although the <offset> |
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and <size> parameters are provided to do partial page mapping, it is |
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recommended that you never use these unless you really know what the |
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cache width is. |
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:: |
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dma_addr_t |
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dma_map_resource(struct device *dev, phys_addr_t phys_addr, size_t size, |
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enum dma_data_direction dir, unsigned long attrs) |
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void |
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dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size, |
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enum dma_data_direction dir, unsigned long attrs) |
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API for mapping and unmapping for MMIO resources. All the notes and |
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warnings for the other mapping APIs apply here. The API should only be |
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used to map device MMIO resources, mapping of RAM is not permitted. |
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:: |
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int |
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dma_mapping_error(struct device *dev, dma_addr_t dma_addr) |
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In some circumstances dma_map_single(), dma_map_page() and dma_map_resource() |
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will fail to create a mapping. A driver can check for these errors by testing |
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the returned DMA address with dma_mapping_error(). A non-zero return value |
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means the mapping could not be created and the driver should take appropriate |
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action (e.g. reduce current DMA mapping usage or delay and try again later). |
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:: |
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int |
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dma_map_sg(struct device *dev, struct scatterlist *sg, |
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int nents, enum dma_data_direction direction) |
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Returns: the number of DMA address segments mapped (this may be shorter |
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than <nents> passed in if some elements of the scatter/gather list are |
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physically or virtually adjacent and an IOMMU maps them with a single |
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entry). |
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Please note that the sg cannot be mapped again if it has been mapped once. |
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The mapping process is allowed to destroy information in the sg. |
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As with the other mapping interfaces, dma_map_sg() can fail. When it |
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does, 0 is returned and a driver must take appropriate action. It is |
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critical that the driver do something, in the case of a block driver |
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aborting the request or even oopsing is better than doing nothing and |
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corrupting the filesystem. |
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With scatterlists, you use the resulting mapping like this:: |
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int i, count = dma_map_sg(dev, sglist, nents, direction); |
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struct scatterlist *sg; |
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for_each_sg(sglist, sg, count, i) { |
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hw_address[i] = sg_dma_address(sg); |
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hw_len[i] = sg_dma_len(sg); |
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} |
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where nents is the number of entries in the sglist. |
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The implementation is free to merge several consecutive sglist entries |
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into one (e.g. with an IOMMU, or if several pages just happen to be |
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physically contiguous) and returns the actual number of sg entries it |
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mapped them to. On failure 0, is returned. |
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Then you should loop count times (note: this can be less than nents times) |
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and use sg_dma_address() and sg_dma_len() macros where you previously |
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accessed sg->address and sg->length as shown above. |
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:: |
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void |
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dma_unmap_sg(struct device *dev, struct scatterlist *sg, |
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int nents, enum dma_data_direction direction) |
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Unmap the previously mapped scatter/gather list. All the parameters |
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must be the same as those and passed in to the scatter/gather mapping |
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API. |
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Note: <nents> must be the number you passed in, *not* the number of |
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DMA address entries returned. |
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:: |
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void |
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dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle, |
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size_t size, |
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enum dma_data_direction direction) |
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void |
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dma_sync_single_for_device(struct device *dev, dma_addr_t dma_handle, |
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size_t size, |
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enum dma_data_direction direction) |
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void |
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dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, |
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int nents, |
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enum dma_data_direction direction) |
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void |
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dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, |
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int nents, |
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enum dma_data_direction direction) |
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Synchronise a single contiguous or scatter/gather mapping for the CPU |
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and device. With the sync_sg API, all the parameters must be the same |
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as those passed into the single mapping API. With the sync_single API, |
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you can use dma_handle and size parameters that aren't identical to |
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those passed into the single mapping API to do a partial sync. |
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.. note:: |
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You must do this: |
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- Before reading values that have been written by DMA from the device |
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(use the DMA_FROM_DEVICE direction) |
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- After writing values that will be written to the device using DMA |
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(use the DMA_TO_DEVICE) direction |
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- before *and* after handing memory to the device if the memory is |
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DMA_BIDIRECTIONAL |
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See also dma_map_single(). |
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:: |
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dma_addr_t |
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dma_map_single_attrs(struct device *dev, void *cpu_addr, size_t size, |
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enum dma_data_direction dir, |
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unsigned long attrs) |
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void |
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dma_unmap_single_attrs(struct device *dev, dma_addr_t dma_addr, |
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size_t size, enum dma_data_direction dir, |
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unsigned long attrs) |
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int |
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dma_map_sg_attrs(struct device *dev, struct scatterlist *sgl, |
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int nents, enum dma_data_direction dir, |
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unsigned long attrs) |
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void |
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dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sgl, |
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int nents, enum dma_data_direction dir, |
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unsigned long attrs) |
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The four functions above are just like the counterpart functions |
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without the _attrs suffixes, except that they pass an optional |
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dma_attrs. |
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The interpretation of DMA attributes is architecture-specific, and |
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each attribute should be documented in |
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Documentation/core-api/dma-attributes.rst. |
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|
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If dma_attrs are 0, the semantics of each of these functions |
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is identical to those of the corresponding function |
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without the _attrs suffix. As a result dma_map_single_attrs() |
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can generally replace dma_map_single(), etc. |
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As an example of the use of the ``*_attrs`` functions, here's how |
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you could pass an attribute DMA_ATTR_FOO when mapping memory |
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for DMA:: |
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#include <linux/dma-mapping.h> |
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/* DMA_ATTR_FOO should be defined in linux/dma-mapping.h and |
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* documented in Documentation/core-api/dma-attributes.rst */ |
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... |
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unsigned long attr; |
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attr |= DMA_ATTR_FOO; |
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.... |
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n = dma_map_sg_attrs(dev, sg, nents, DMA_TO_DEVICE, attr); |
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.... |
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Architectures that care about DMA_ATTR_FOO would check for its |
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presence in their implementations of the mapping and unmapping |
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routines, e.g.::: |
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void whizco_dma_map_sg_attrs(struct device *dev, dma_addr_t dma_addr, |
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size_t size, enum dma_data_direction dir, |
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unsigned long attrs) |
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{ |
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.... |
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if (attrs & DMA_ATTR_FOO) |
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/* twizzle the frobnozzle */ |
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.... |
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} |
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Part II - Non-coherent DMA allocations |
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-------------------------------------- |
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These APIs allow to allocate pages that are guaranteed to be DMA addressable |
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by the passed in device, but which need explicit management of memory ownership |
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for the kernel vs the device. |
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If you don't understand how cache line coherency works between a processor and |
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an I/O device, you should not be using this part of the API. |
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:: |
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struct page * |
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dma_alloc_pages(struct device *dev, size_t size, dma_addr_t *dma_handle, |
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enum dma_data_direction dir, gfp_t gfp) |
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|
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This routine allocates a region of <size> bytes of non-coherent memory. It |
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returns a pointer to first struct page for the region, or NULL if the |
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allocation failed. The resulting struct page can be used for everything a |
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struct page is suitable for. |
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|
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It also returns a <dma_handle> which may be cast to an unsigned integer the |
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same width as the bus and given to the device as the DMA address base of |
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the region. |
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|
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The dir parameter specified if data is read and/or written by the device, |
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see dma_map_single() for details. |
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|
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The gfp parameter allows the caller to specify the ``GFP_`` flags (see |
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kmalloc()) for the allocation, but rejects flags used to specify a memory |
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zone such as GFP_DMA or GFP_HIGHMEM. |
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|
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Before giving the memory to the device, dma_sync_single_for_device() needs |
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to be called, and before reading memory written by the device, |
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dma_sync_single_for_cpu(), just like for streaming DMA mappings that are |
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reused. |
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|
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:: |
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|
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void |
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dma_free_pages(struct device *dev, size_t size, struct page *page, |
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dma_addr_t dma_handle, enum dma_data_direction dir) |
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Free a region of memory previously allocated using dma_alloc_pages(). |
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dev, size, dma_handle and dir must all be the same as those passed into |
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dma_alloc_pages(). page must be the pointer returned by dma_alloc_pages(). |
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|
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:: |
|
|
|
int |
|
dma_mmap_pages(struct device *dev, struct vm_area_struct *vma, |
|
size_t size, struct page *page) |
|
|
|
Map an allocation returned from dma_alloc_pages() into a user address space. |
|
dev and size must be the same as those passed into dma_alloc_pages(). |
|
page must be the pointer returned by dma_alloc_pages(). |
|
|
|
:: |
|
|
|
void * |
|
dma_alloc_noncoherent(struct device *dev, size_t size, |
|
dma_addr_t *dma_handle, enum dma_data_direction dir, |
|
gfp_t gfp) |
|
|
|
This routine is a convenient wrapper around dma_alloc_pages that returns the |
|
kernel virtual address for the allocated memory instead of the page structure. |
|
|
|
:: |
|
|
|
void |
|
dma_free_noncoherent(struct device *dev, size_t size, void *cpu_addr, |
|
dma_addr_t dma_handle, enum dma_data_direction dir) |
|
|
|
Free a region of memory previously allocated using dma_alloc_noncoherent(). |
|
dev, size, 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 |
|
dma_alloc_noncoherent(). |
|
|
|
:: |
|
|
|
struct sg_table * |
|
dma_alloc_noncontiguous(struct device *dev, size_t size, |
|
enum dma_data_direction dir, gfp_t gfp, |
|
unsigned long attrs); |
|
|
|
This routine allocates <size> bytes of non-coherent and possibly non-contiguous |
|
memory. It returns a pointer to struct sg_table that describes the allocated |
|
and DMA mapped memory, or NULL if the allocation failed. The resulting memory |
|
can be used for struct page mapped into a scatterlist are suitable for. |
|
|
|
The return sg_table is guaranteed to have 1 single DMA mapped segment as |
|
indicated by sgt->nents, but it might have multiple CPU side segments as |
|
indicated by sgt->orig_nents. |
|
|
|
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. |
|
|
|
The attrs argument must be either 0 or DMA_ATTR_ALLOC_SINGLE_PAGES. |
|
|
|
Before giving the memory to the device, dma_sync_sgtable_for_device() needs |
|
to be called, and before reading memory written by the device, |
|
dma_sync_sgtable_for_cpu(), just like for streaming DMA mappings that are |
|
reused. |
|
|
|
:: |
|
|
|
void |
|
dma_free_noncontiguous(struct device *dev, size_t size, |
|
struct sg_table *sgt, |
|
enum dma_data_direction dir) |
|
|
|
Free memory previously allocated using dma_alloc_noncontiguous(). dev, size, |
|
and dir must all be the same as those passed into dma_alloc_noncontiguous(). |
|
sgt must be the pointer returned by dma_alloc_noncontiguous(). |
|
|
|
:: |
|
|
|
void * |
|
dma_vmap_noncontiguous(struct device *dev, size_t size, |
|
struct sg_table *sgt) |
|
|
|
Return a contiguous kernel mapping for an allocation returned from |
|
dma_alloc_noncontiguous(). dev and size must be the same as those passed into |
|
dma_alloc_noncontiguous(). sgt must be the pointer returned by |
|
dma_alloc_noncontiguous(). |
|
|
|
Once a non-contiguous allocation is mapped using this function, the |
|
flush_kernel_vmap_range() and invalidate_kernel_vmap_range() APIs must be used |
|
to manage the coherency between the kernel mapping, the device and user space |
|
mappings (if any). |
|
|
|
:: |
|
|
|
void |
|
dma_vunmap_noncontiguous(struct device *dev, void *vaddr) |
|
|
|
Unmap a kernel mapping returned by dma_vmap_noncontiguous(). dev must be the |
|
same the one passed into dma_alloc_noncontiguous(). vaddr must be the pointer |
|
returned by dma_vmap_noncontiguous(). |
|
|
|
|
|
:: |
|
|
|
int |
|
dma_mmap_noncontiguous(struct device *dev, struct vm_area_struct *vma, |
|
size_t size, struct sg_table *sgt) |
|
|
|
Map an allocation returned from dma_alloc_noncontiguous() into a user address |
|
space. dev and size must be the same as those passed into |
|
dma_alloc_noncontiguous(). sgt must be the pointer returned by |
|
dma_alloc_noncontiguous(). |
|
|
|
:: |
|
|
|
int |
|
dma_get_cache_alignment(void) |
|
|
|
Returns the processor cache alignment. This is the absolute minimum |
|
alignment *and* width that you must observe when either mapping |
|
memory or doing partial flushes. |
|
|
|
.. note:: |
|
|
|
This API may return a number *larger* than the actual cache |
|
line, but it will guarantee that one or more cache lines fit exactly |
|
into the width returned by this call. It will also always be a power |
|
of two for easy alignment. |
|
|
|
|
|
Part III - Debug drivers use of the DMA-API |
|
------------------------------------------- |
|
|
|
The DMA-API as described above has some constraints. DMA addresses must be |
|
released with the corresponding function with the same size for example. With |
|
the advent of hardware IOMMUs it becomes more and more important that drivers |
|
do not violate those constraints. In the worst case such a violation can |
|
result in data corruption up to destroyed filesystems. |
|
|
|
To debug drivers and find bugs in the usage of the DMA-API checking code can |
|
be compiled into the kernel which will tell the developer about those |
|
violations. If your architecture supports it you can select the "Enable |
|
debugging of DMA-API usage" option in your kernel configuration. Enabling this |
|
option has a performance impact. Do not enable it in production kernels. |
|
|
|
If you boot the resulting kernel will contain code which does some bookkeeping |
|
about what DMA memory was allocated for which device. If this code detects an |
|
error it prints a warning message with some details into your kernel log. An |
|
example warning message may look like this:: |
|
|
|
WARNING: at /data2/repos/linux-2.6-iommu/lib/dma-debug.c:448 |
|
check_unmap+0x203/0x490() |
|
Hardware name: |
|
forcedeth 0000:00:08.0: DMA-API: device driver frees DMA memory with wrong |
|
function [device address=0x00000000640444be] [size=66 bytes] [mapped as |
|
single] [unmapped as page] |
|
Modules linked in: nfsd exportfs bridge stp llc r8169 |
|
Pid: 0, comm: swapper Tainted: G W 2.6.28-dmatest-09289-g8bb99c0 #1 |
|
Call Trace: |
|
<IRQ> [<ffffffff80240b22>] warn_slowpath+0xf2/0x130 |
|
[<ffffffff80647b70>] _spin_unlock+0x10/0x30 |
|
[<ffffffff80537e75>] usb_hcd_link_urb_to_ep+0x75/0xc0 |
|
[<ffffffff80647c22>] _spin_unlock_irqrestore+0x12/0x40 |
|
[<ffffffff8055347f>] ohci_urb_enqueue+0x19f/0x7c0 |
|
[<ffffffff80252f96>] queue_work+0x56/0x60 |
|
[<ffffffff80237e10>] enqueue_task_fair+0x20/0x50 |
|
[<ffffffff80539279>] usb_hcd_submit_urb+0x379/0xbc0 |
|
[<ffffffff803b78c3>] cpumask_next_and+0x23/0x40 |
|
[<ffffffff80235177>] find_busiest_group+0x207/0x8a0 |
|
[<ffffffff8064784f>] _spin_lock_irqsave+0x1f/0x50 |
|
[<ffffffff803c7ea3>] check_unmap+0x203/0x490 |
|
[<ffffffff803c8259>] debug_dma_unmap_page+0x49/0x50 |
|
[<ffffffff80485f26>] nv_tx_done_optimized+0xc6/0x2c0 |
|
[<ffffffff80486c13>] nv_nic_irq_optimized+0x73/0x2b0 |
|
[<ffffffff8026df84>] handle_IRQ_event+0x34/0x70 |
|
[<ffffffff8026ffe9>] handle_edge_irq+0xc9/0x150 |
|
[<ffffffff8020e3ab>] do_IRQ+0xcb/0x1c0 |
|
[<ffffffff8020c093>] ret_from_intr+0x0/0xa |
|
<EOI> <4>---[ end trace f6435a98e2a38c0e ]--- |
|
|
|
The driver developer can find the driver and the device including a stacktrace |
|
of the DMA-API call which caused this warning. |
|
|
|
Per default only the first error will result in a warning message. All other |
|
errors will only silently counted. This limitation exist to prevent the code |
|
from flooding your kernel log. To support debugging a device driver this can |
|
be disabled via debugfs. See the debugfs interface documentation below for |
|
details. |
|
|
|
The debugfs directory for the DMA-API debugging code is called dma-api/. In |
|
this directory the following files can currently be found: |
|
|
|
=============================== =============================================== |
|
dma-api/all_errors This file contains a numeric value. If this |
|
value is not equal to zero the debugging code |
|
will print a warning for every error it finds |
|
into the kernel log. Be careful with this |
|
option, as it can easily flood your logs. |
|
|
|
dma-api/disabled This read-only file contains the character 'Y' |
|
if the debugging code is disabled. This can |
|
happen when it runs out of memory or if it was |
|
disabled at boot time |
|
|
|
dma-api/dump This read-only file contains current DMA |
|
mappings. |
|
|
|
dma-api/error_count This file is read-only and shows the total |
|
numbers of errors found. |
|
|
|
dma-api/num_errors The number in this file shows how many |
|
warnings will be printed to the kernel log |
|
before it stops. This number is initialized to |
|
one at system boot and be set by writing into |
|
this file |
|
|
|
dma-api/min_free_entries This read-only file can be read to get the |
|
minimum number of free dma_debug_entries the |
|
allocator has ever seen. If this value goes |
|
down to zero the code will attempt to increase |
|
nr_total_entries to compensate. |
|
|
|
dma-api/num_free_entries The current number of free dma_debug_entries |
|
in the allocator. |
|
|
|
dma-api/nr_total_entries The total number of dma_debug_entries in the |
|
allocator, both free and used. |
|
|
|
dma-api/driver_filter You can write a name of a driver into this file |
|
to limit the debug output to requests from that |
|
particular driver. Write an empty string to |
|
that file to disable the filter and see |
|
all errors again. |
|
=============================== =============================================== |
|
|
|
If you have this code compiled into your kernel it will be enabled by default. |
|
If you want to boot without the bookkeeping anyway you can provide |
|
'dma_debug=off' as a boot parameter. This will disable DMA-API debugging. |
|
Notice that you can not enable it again at runtime. You have to reboot to do |
|
so. |
|
|
|
If you want to see debug messages only for a special device driver you can |
|
specify the dma_debug_driver=<drivername> parameter. This will enable the |
|
driver filter at boot time. The debug code will only print errors for that |
|
driver afterwards. This filter can be disabled or changed later using debugfs. |
|
|
|
When the code disables itself at runtime this is most likely because it ran |
|
out of dma_debug_entries and was unable to allocate more on-demand. 65536 |
|
entries are preallocated at boot - if this is too low for you boot with |
|
'dma_debug_entries=<your_desired_number>' to overwrite the default. Note |
|
that the code allocates entries in batches, so the exact number of |
|
preallocated entries may be greater than the actual number requested. The |
|
code will print to the kernel log each time it has dynamically allocated |
|
as many entries as were initially preallocated. This is to indicate that a |
|
larger preallocation size may be appropriate, or if it happens continually |
|
that a driver may be leaking mappings. |
|
|
|
:: |
|
|
|
void |
|
debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr); |
|
|
|
dma-debug interface debug_dma_mapping_error() to debug drivers that fail |
|
to check DMA mapping errors on addresses returned by dma_map_single() and |
|
dma_map_page() interfaces. This interface clears a flag set by |
|
debug_dma_map_page() to indicate that dma_mapping_error() has been called by |
|
the driver. When driver does unmap, debug_dma_unmap() checks the flag and if |
|
this flag is still set, prints warning message that includes call trace that |
|
leads up to the unmap. This interface can be called from dma_mapping_error() |
|
routines to enable DMA mapping error check debugging.
|
|
|