DMA-API.txt: standardize document format
Each text file under Documentation follows a different format. Some doesn't even have titles! Change its representation to follow the adopted standard, using ReST markups for it to be parseable by Sphinx: - Fix some title marks to match ReST; - use :Author: for author name; - foo_ is an hyperlink. Get rid of it; - Mark literal blocks as such; - Use tables on some places that are almost using the table format. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mauro Carvalho Chehab
Jonathan Corbet
parent
a2fbbcea7b
commit
03158a70ad
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@ -1,7 +1,8 @@
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Dynamic DMA mapping using the generic device
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============================================
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============================================
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Dynamic DMA mapping using the generic device
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============================================
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James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
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:Author: James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
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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/DMA-API-HOWTO.txt.
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@ -12,10 +13,10 @@ 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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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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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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@ -26,9 +27,11 @@ 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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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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::
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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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@ -51,20 +54,24 @@ 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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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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void *
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dma_zalloc_coherent(struct device *dev, size_t size,
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dma_addr_t *dma_handle, gfp_t flag)
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::
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void *
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dma_zalloc_coherent(struct device *dev, size_t size,
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dma_addr_t *dma_handle, gfp_t flag)
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Wraps dma_alloc_coherent() and also zeroes the returned memory if the
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allocation attempt succeeded.
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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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::
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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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@ -78,7 +85,7 @@ 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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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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@ -88,6 +95,8 @@ 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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@ -103,16 +112,21 @@ 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 *dma_pool_zalloc(struct dma_pool *pool, gfp_t mem_flags,
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dma_addr_t *handle)
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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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void *dma_pool_alloc(struct dma_pool *pool, gfp_t gfp_flags,
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dma_addr_t *dma_handle);
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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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@ -122,16 +136,20 @@ 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 dma_pool_free(struct dma_pool *pool, void *vaddr,
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dma_addr_t addr);
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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 dma_pool_destroy(struct dma_pool *pool);
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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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@ -141,32 +159,40 @@ 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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int
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dma_set_mask_and_coherent(struct device *dev, u64 mask)
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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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int
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dma_set_mask(struct device *dev, u64 mask)
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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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int
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dma_set_coherent_mask(struct device *dev, u64 mask)
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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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u64
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dma_get_required_mask(struct device *dev)
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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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@ -182,94 +208,107 @@ call to set the mask to the value returned.
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Part Id - Streaming DMA mappings
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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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::
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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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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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Notes: 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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.. note::
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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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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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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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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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Warnings: 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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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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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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.. warning::
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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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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_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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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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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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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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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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::
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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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@ -277,20 +316,24 @@ 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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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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::
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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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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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int
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dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
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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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@ -298,9 +341,11 @@ 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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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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@ -316,7 +361,7 @@ 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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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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@ -337,9 +382,11 @@ 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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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
|
||||
|
|
@ -348,18 +395,27 @@ API.
|
|||
Note: <nents> must be the number you passed in, *not* the number of
|
||||
DMA address entries returned.
|
||||
|
||||
void
|
||||
dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle, size_t size,
|
||||
enum dma_data_direction direction)
|
||||
void
|
||||
dma_sync_single_for_device(struct device *dev, dma_addr_t dma_handle, size_t size,
|
||||
enum dma_data_direction direction)
|
||||
void
|
||||
dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, int nents,
|
||||
enum dma_data_direction direction)
|
||||
void
|
||||
dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, int nents,
|
||||
enum dma_data_direction direction)
|
||||
::
|
||||
|
||||
void
|
||||
dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle,
|
||||
size_t size,
|
||||
enum dma_data_direction direction)
|
||||
|
||||
void
|
||||
dma_sync_single_for_device(struct device *dev, dma_addr_t dma_handle,
|
||||
size_t size,
|
||||
enum dma_data_direction direction)
|
||||
|
||||
void
|
||||
dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
|
||||
int nents,
|
||||
enum dma_data_direction direction)
|
||||
|
||||
void
|
||||
dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
|
||||
int nents,
|
||||
enum dma_data_direction direction)
|
||||
|
||||
Synchronise a single contiguous or scatter/gather mapping for the CPU
|
||||
and device. With the sync_sg API, all the parameters must be the same
|
||||
|
|
@ -367,36 +423,41 @@ as those passed into the single mapping API. With the sync_single API,
|
|||
you can use dma_handle and size parameters that aren't identical to
|
||||
those passed into the single mapping API to do a partial sync.
|
||||
|
||||
Notes: You must do this:
|
||||
|
||||
- Before reading values that have been written by DMA from the device
|
||||
(use the DMA_FROM_DEVICE direction)
|
||||
- After writing values that will be written to the device using DMA
|
||||
(use the DMA_TO_DEVICE) direction
|
||||
- before *and* after handing memory to the device if the memory is
|
||||
DMA_BIDIRECTIONAL
|
||||
.. note::
|
||||
|
||||
You must do this:
|
||||
|
||||
- Before reading values that have been written by DMA from the device
|
||||
(use the DMA_FROM_DEVICE direction)
|
||||
- After writing values that will be written to the device using DMA
|
||||
(use the DMA_TO_DEVICE) direction
|
||||
- before *and* after handing memory to the device if the memory is
|
||||
DMA_BIDIRECTIONAL
|
||||
|
||||
See also dma_map_single().
|
||||
|
||||
dma_addr_t
|
||||
dma_map_single_attrs(struct device *dev, void *cpu_addr, size_t size,
|
||||
enum dma_data_direction dir,
|
||||
unsigned long attrs)
|
||||
::
|
||||
|
||||
void
|
||||
dma_unmap_single_attrs(struct device *dev, dma_addr_t dma_addr,
|
||||
size_t size, enum dma_data_direction dir,
|
||||
unsigned long attrs)
|
||||
dma_addr_t
|
||||
dma_map_single_attrs(struct device *dev, void *cpu_addr, size_t size,
|
||||
enum dma_data_direction dir,
|
||||
unsigned long attrs)
|
||||
|
||||
int
|
||||
dma_map_sg_attrs(struct device *dev, struct scatterlist *sgl,
|
||||
int nents, enum dma_data_direction dir,
|
||||
unsigned long attrs)
|
||||
void
|
||||
dma_unmap_single_attrs(struct device *dev, dma_addr_t dma_addr,
|
||||
size_t size, enum dma_data_direction dir,
|
||||
unsigned long attrs)
|
||||
|
||||
void
|
||||
dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sgl,
|
||||
int nents, enum dma_data_direction dir,
|
||||
unsigned long attrs)
|
||||
int
|
||||
dma_map_sg_attrs(struct device *dev, struct scatterlist *sgl,
|
||||
int nents, enum dma_data_direction dir,
|
||||
unsigned long attrs)
|
||||
|
||||
void
|
||||
dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sgl,
|
||||
int nents, enum dma_data_direction dir,
|
||||
unsigned long attrs)
|
||||
|
||||
The four functions above are just like the counterpart functions
|
||||
without the _attrs suffixes, except that they pass an optional
|
||||
|
|
@ -410,37 +471,38 @@ is identical to those of the corresponding function
|
|||
without the _attrs suffix. As a result dma_map_single_attrs()
|
||||
can generally replace dma_map_single(), etc.
|
||||
|
||||
As an example of the use of the *_attrs functions, here's how
|
||||
As an example of the use of the ``*_attrs`` functions, here's how
|
||||
you could pass an attribute DMA_ATTR_FOO when mapping memory
|
||||
for DMA:
|
||||
for DMA::
|
||||
|
||||
#include <linux/dma-mapping.h>
|
||||
/* DMA_ATTR_FOO should be defined in linux/dma-mapping.h and
|
||||
* documented in Documentation/DMA-attributes.txt */
|
||||
...
|
||||
#include <linux/dma-mapping.h>
|
||||
/* DMA_ATTR_FOO should be defined in linux/dma-mapping.h and
|
||||
* documented in Documentation/DMA-attributes.txt */
|
||||
...
|
||||
|
||||
unsigned long attr;
|
||||
attr |= DMA_ATTR_FOO;
|
||||
....
|
||||
n = dma_map_sg_attrs(dev, sg, nents, DMA_TO_DEVICE, attr);
|
||||
....
|
||||
unsigned long attr;
|
||||
attr |= DMA_ATTR_FOO;
|
||||
....
|
||||
n = dma_map_sg_attrs(dev, sg, nents, DMA_TO_DEVICE, attr);
|
||||
....
|
||||
|
||||
Architectures that care about DMA_ATTR_FOO would check for its
|
||||
presence in their implementations of the mapping and unmapping
|
||||
routines, e.g.:
|
||||
routines, e.g.:::
|
||||
|
||||
void whizco_dma_map_sg_attrs(struct device *dev, dma_addr_t dma_addr,
|
||||
size_t size, enum dma_data_direction dir,
|
||||
unsigned long attrs)
|
||||
{
|
||||
....
|
||||
if (attrs & DMA_ATTR_FOO)
|
||||
/* twizzle the frobnozzle */
|
||||
....
|
||||
void whizco_dma_map_sg_attrs(struct device *dev, dma_addr_t dma_addr,
|
||||
size_t size, enum dma_data_direction dir,
|
||||
unsigned long attrs)
|
||||
{
|
||||
....
|
||||
if (attrs & DMA_ATTR_FOO)
|
||||
/* twizzle the frobnozzle */
|
||||
....
|
||||
}
|
||||
|
||||
|
||||
Part II - Advanced dma_ usage
|
||||
-----------------------------
|
||||
Part II - Advanced dma usage
|
||||
----------------------------
|
||||
|
||||
Warning: These pieces of the DMA API should not be used in the
|
||||
majority of cases, since they cater for unlikely corner cases that
|
||||
|
|
@ -450,9 +512,11 @@ 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 at all.
|
||||
|
||||
void *
|
||||
dma_alloc_noncoherent(struct device *dev, size_t size,
|
||||
dma_addr_t *dma_handle, gfp_t flag)
|
||||
::
|
||||
|
||||
void *
|
||||
dma_alloc_noncoherent(struct device *dev, size_t size,
|
||||
dma_addr_t *dma_handle, gfp_t flag)
|
||||
|
||||
Identical to dma_alloc_coherent() except that the platform will
|
||||
choose to return either consistent or non-consistent memory as it sees
|
||||
|
|
@ -468,39 +532,49 @@ only use this API if you positively know your driver will be
|
|||
required to work on one of the rare (usually non-PCI) architectures
|
||||
that simply cannot make consistent memory.
|
||||
|
||||
void
|
||||
dma_free_noncoherent(struct device *dev, size_t size, void *cpu_addr,
|
||||
dma_addr_t dma_handle)
|
||||
::
|
||||
|
||||
void
|
||||
dma_free_noncoherent(struct device *dev, size_t size, void *cpu_addr,
|
||||
dma_addr_t dma_handle)
|
||||
|
||||
Free memory allocated by the nonconsistent API. All parameters must
|
||||
be identical to those passed in (and returned by
|
||||
dma_alloc_noncoherent()).
|
||||
|
||||
int
|
||||
dma_get_cache_alignment(void)
|
||||
::
|
||||
|
||||
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.
|
||||
|
||||
Notes: 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.
|
||||
.. note::
|
||||
|
||||
void
|
||||
dma_cache_sync(struct device *dev, void *vaddr, size_t size,
|
||||
enum dma_data_direction direction)
|
||||
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.
|
||||
|
||||
::
|
||||
|
||||
void
|
||||
dma_cache_sync(struct device *dev, void *vaddr, size_t size,
|
||||
enum dma_data_direction direction)
|
||||
|
||||
Do a partial sync of memory that was allocated by
|
||||
dma_alloc_noncoherent(), starting at virtual address vaddr and
|
||||
continuing on for size. Again, you *must* observe the cache line
|
||||
boundaries when doing this.
|
||||
|
||||
int
|
||||
dma_declare_coherent_memory(struct device *dev, phys_addr_t phys_addr,
|
||||
dma_addr_t device_addr, size_t size, int
|
||||
flags)
|
||||
::
|
||||
|
||||
int
|
||||
dma_declare_coherent_memory(struct device *dev, phys_addr_t phys_addr,
|
||||
dma_addr_t device_addr, size_t size, int
|
||||
flags)
|
||||
|
||||
Declare region of memory to be handed out by dma_alloc_coherent() when
|
||||
it's asked for coherent memory for this device.
|
||||
|
|
@ -516,21 +590,21 @@ size is the size of the area (must be multiples of PAGE_SIZE).
|
|||
|
||||
flags can be ORed together and are:
|
||||
|
||||
DMA_MEMORY_MAP - request that the memory returned from
|
||||
dma_alloc_coherent() be directly writable.
|
||||
- DMA_MEMORY_MAP - request that the memory returned from
|
||||
dma_alloc_coherent() be directly writable.
|
||||
|
||||
DMA_MEMORY_IO - request that the memory returned from
|
||||
dma_alloc_coherent() be addressable using read()/write()/memcpy_toio() etc.
|
||||
- DMA_MEMORY_IO - request that the memory returned from
|
||||
dma_alloc_coherent() be addressable using read()/write()/memcpy_toio() etc.
|
||||
|
||||
One or both of these flags must be present.
|
||||
|
||||
DMA_MEMORY_INCLUDES_CHILDREN - make the declared memory be allocated by
|
||||
dma_alloc_coherent of any child devices of this one (for memory residing
|
||||
on a bridge).
|
||||
- DMA_MEMORY_INCLUDES_CHILDREN - make the declared memory be allocated by
|
||||
dma_alloc_coherent of any child devices of this one (for memory residing
|
||||
on a bridge).
|
||||
|
||||
DMA_MEMORY_EXCLUSIVE - only allocate memory from the declared regions.
|
||||
Do not allow dma_alloc_coherent() to fall back to system memory when
|
||||
it's out of memory in the declared region.
|
||||
- DMA_MEMORY_EXCLUSIVE - only allocate memory from the declared regions.
|
||||
Do not allow dma_alloc_coherent() to fall back to system memory when
|
||||
it's out of memory in the declared region.
|
||||
|
||||
The return value will be either DMA_MEMORY_MAP or DMA_MEMORY_IO and
|
||||
must correspond to a passed in flag (i.e. no returning DMA_MEMORY_IO
|
||||
|
|
@ -543,15 +617,17 @@ must be accessed using the correct bus functions. If your driver
|
|||
isn't prepared to handle this contingency, it should not specify
|
||||
DMA_MEMORY_IO in the input flags.
|
||||
|
||||
As a simplification for the platforms, only *one* such region of
|
||||
As a simplification for the platforms, only **one** such region of
|
||||
memory may be declared per device.
|
||||
|
||||
For reasons of efficiency, most platforms choose to track the declared
|
||||
region only at the granularity of a page. For smaller allocations,
|
||||
you should use the dma_pool() API.
|
||||
|
||||
void
|
||||
dma_release_declared_memory(struct device *dev)
|
||||
::
|
||||
|
||||
void
|
||||
dma_release_declared_memory(struct device *dev)
|
||||
|
||||
Remove the memory region previously declared from the system. This
|
||||
API performs *no* in-use checking for this region and will return
|
||||
|
|
@ -559,9 +635,11 @@ unconditionally having removed all the required structures. It is the
|
|||
driver's job to ensure that no parts of this memory region are
|
||||
currently in use.
|
||||
|
||||
void *
|
||||
dma_mark_declared_memory_occupied(struct device *dev,
|
||||
dma_addr_t device_addr, size_t size)
|
||||
::
|
||||
|
||||
void *
|
||||
dma_mark_declared_memory_occupied(struct device *dev,
|
||||
dma_addr_t device_addr, size_t size)
|
||||
|
||||
This is used to occupy specific regions of the declared space
|
||||
(dma_alloc_coherent() will hand out the first free region it finds).
|
||||
|
|
@ -592,38 +670,37 @@ 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:
|
||||
example warning message may look like this::
|
||||
|
||||
------------[ cut here ]------------
|
||||
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 ]---
|
||||
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.
|
||||
|
|
@ -637,43 +714,42 @@ 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
|
||||
=============================== ===============================================
|
||||
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'
|
||||
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/error_count This file is read-only and shows the total
|
||||
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
|
||||
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
|
||||
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 disable itself
|
||||
because it is not longer reliable.
|
||||
|
||||
dma-api/num_free_entries
|
||||
The current number of free dma_debug_entries
|
||||
dma-api/num_free_entries The current number of free dma_debug_entries
|
||||
in the allocator.
|
||||
|
||||
dma-api/driver-filter
|
||||
You can write a name of a driver into this file
|
||||
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
|
||||
|
|
@ -692,7 +768,10 @@ of preallocated entries is defined per architecture. If it is too low for you
|
|||
boot with 'dma_debug_entries=<your_desired_number>' to overwrite the
|
||||
architectural default.
|
||||
|
||||
void debug_dma_mapping_error(struct device *dev, dma_addr_t dma_addr);
|
||||
::
|
||||
|
||||
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
|
||||
|
|
@ -702,4 +781,3 @@ 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.
|
||||
|
||||
|
|
|
|||
Loading…
Reference in New Issue