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Doc: DMA-API update

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Fix typos and update function parameters.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Muli Ben-Yehuda <muli@il.ibm.com>
Cc: James Bottomley <James.Bottomley@steeleye.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Randy Dunlap 2007-07-31 00:38:17 -07:00 committed by Linus Torvalds
parent 9eb3ff4037
commit a12e2c6cde
1 changed files with 38 additions and 41 deletions
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79
Documentation/DMA-API.txt
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@ -26,7 +26,7 @@ Part Ia - Using large dma-coherent buffers
void * void *
dma_alloc_coherent(struct device *dev, size_t size, dma_alloc_coherent(struct device *dev, size_t size,
dma_addr_t *dma_handle, int flag) dma_addr_t *dma_handle, gfp_t flag)
void * void *
pci_alloc_consistent(struct pci_dev *dev, size_t size, pci_alloc_consistent(struct pci_dev *dev, size_t size,
dma_addr_t *dma_handle) dma_addr_t *dma_handle)
@ -38,7 +38,7 @@ to make sure to flush the processor's write buffers before telling
devices to read that memory.) devices to read that memory.)
This routine allocates a region of <size> bytes of consistent memory. This routine allocates a region of <size> bytes of consistent memory.
it also returns a <dma_handle> which may be cast to an unsigned It also returns a <dma_handle> which may be cast to an unsigned
integer the same width as the bus and used as the physical address integer the same width as the bus and used as the physical address
base of the region. base of the region.
@ -52,21 +52,21 @@ The simplest way to do that is to use the dma_pool calls (see below).
The flag parameter (dma_alloc_coherent only) allows the caller to The flag parameter (dma_alloc_coherent only) allows the caller to
specify the GFP_ flags (see kmalloc) for the allocation (the specify the GFP_ flags (see kmalloc) for the allocation (the
implementation may chose to ignore flags that affect the location of implementation may choose to ignore flags that affect the location of
the returned memory, like GFP_DMA). For pci_alloc_consistent, you the returned memory, like GFP_DMA). For pci_alloc_consistent, you
must assume GFP_ATOMIC behaviour. must assume GFP_ATOMIC behaviour.
void void
dma_free_coherent(struct device *dev, size_t size, void *cpu_addr dma_free_coherent(struct device *dev, size_t size, void *cpu_addr,
dma_addr_t dma_handle) dma_addr_t dma_handle)
void void
pci_free_consistent(struct pci_dev *dev, size_t size, void *cpu_addr pci_free_consistent(struct pci_dev *dev, size_t size, void *cpu_addr,
dma_addr_t dma_handle) dma_addr_t dma_handle)
Free the region of consistent memory you previously allocated. dev, Free the region of consistent memory you previously allocated. dev,
size and dma_handle must all be the same as those passed into the size and dma_handle must all be the same as those passed into the
consistent allocate. cpu_addr must be the virtual address returned by consistent allocate. cpu_addr must be the virtual address returned by
the consistent allocate the consistent allocate.
Part Ib - Using small dma-coherent buffers Part Ib - Using small dma-coherent buffers
@ -77,9 +77,9 @@ To get this part of the dma_ API, you must #include <linux/dmapool.h>
Many drivers need lots of small dma-coherent memory regions for DMA Many drivers need lots of small dma-coherent memory regions for DMA
descriptors or I/O buffers. Rather than allocating in units of a page descriptors or I/O buffers. Rather than allocating in units of a page
or more using dma_alloc_coherent(), you can use DMA pools. These work or more using dma_alloc_coherent(), you can use DMA pools. These work
much like a struct kmem_cache, except that they use the dma-coherent allocator much like a struct kmem_cache, except that they use the dma-coherent allocator,
not __get_free_pages(). Also, they understand common hardware constraints not __get_free_pages(). Also, they understand common hardware constraints
for alignment, like queue heads needing to be aligned on N byte boundaries. for alignment, like queue heads needing to be aligned on N-byte boundaries.
struct dma_pool * struct dma_pool *
@ -102,15 +102,15 @@ crossing restrictions, pass 0 for alloc; passing 4096 says memory allocated
from this pool must not cross 4KByte boundaries. from this pool must not cross 4KByte boundaries.
void *dma_pool_alloc(struct dma_pool *pool, int gfp_flags, void *dma_pool_alloc(struct dma_pool *pool, gfp_t gfp_flags,
dma_addr_t *dma_handle); dma_addr_t *dma_handle);
void *pci_pool_alloc(struct pci_pool *pool, int gfp_flags, void *pci_pool_alloc(struct pci_pool *pool, gfp_t gfp_flags,
dma_addr_t *dma_handle); dma_addr_t *dma_handle);
This allocates memory from the pool; the returned memory will meet the size This allocates memory from the pool; the returned memory will meet the size
and alignment requirements specified at creation time. Pass GFP_ATOMIC to and alignment requirements specified at creation time. Pass GFP_ATOMIC to
prevent blocking, or if it's permitted (not in_interrupt, not holding SMP locks) prevent blocking, or if it's permitted (not in_interrupt, not holding SMP locks),
pass GFP_KERNEL to allow blocking. Like dma_alloc_coherent(), this returns pass GFP_KERNEL to allow blocking. Like dma_alloc_coherent(), this returns
two values: an address usable by the cpu, and the dma address usable by the two values: an address usable by the cpu, and the dma address usable by the
pool's device. pool's device.
@ -123,7 +123,7 @@ pool's device.
dma_addr_t addr); dma_addr_t addr);
This puts memory back into the pool. The pool is what was passed to This puts memory back into the pool. The pool is what was passed to
the pool allocation routine; the cpu and dma addresses are what the pool allocation routine; the cpu (vaddr) and dma addresses are what
were returned when that routine allocated the memory being freed. were returned when that routine allocated the memory being freed.
@ -209,18 +209,18 @@ Notes: Not all memory regions in a machine can be mapped by this
API. Further, regions that appear to be physically contiguous in API. Further, regions that appear to be physically contiguous in
kernel virtual space may not be contiguous as physical memory. Since kernel virtual space may not be contiguous as physical memory. Since
this API does not provide any scatter/gather capability, it will fail this API does not provide any scatter/gather capability, it will fail
if the user tries to map a non physically contiguous piece of memory. if the user tries to map a non-physically contiguous piece of memory.
For this reason, it is recommended that memory mapped by this API be For this reason, it is recommended that memory mapped by this API be
obtained only from sources which guarantee to be physically contiguous obtained only from sources which guarantee it to be physically contiguous
(like kmalloc). (like kmalloc).
Further, the physical address of the memory must be within the Further, the physical address of the memory must be within the
dma_mask of the device (the dma_mask represents a bit mask of the dma_mask of the device (the dma_mask represents a bit mask of the
addressable region for the device. i.e. if the physical address of addressable region for the device. I.e., if the physical address of
the memory anded with the dma_mask is still equal to the physical the memory anded with the dma_mask is still equal to the physical
address, then the device can perform DMA to the memory). In order to address, then the device can perform DMA to the memory). In order to
ensure that the memory allocated by kmalloc is within the dma_mask, ensure that the memory allocated by kmalloc is within the dma_mask,
the driver may specify various platform dependent flags to restrict the driver may specify various platform-dependent flags to restrict
the physical memory range of the allocation (e.g. on x86, GFP_DMA the physical memory range of the allocation (e.g. on x86, GFP_DMA
guarantees to be within the first 16Mb of available physical memory, guarantees to be within the first 16Mb of available physical memory,
as required by ISA devices). as required by ISA devices).
@ -244,14 +244,14 @@ are guaranteed also to be cache line boundaries).
DMA_TO_DEVICE synchronisation must be done after the last modification DMA_TO_DEVICE synchronisation must be done after the last modification
of the memory region by the software and before it is handed off to of the memory region by the software and before it is handed off to
the driver. Once this primitive is used. Memory covered by this the driver. Once this primitive is used, memory covered by this
primitive should be treated as read only by the device. If the device primitive should be treated as read-only by the device. If the device
may write to it at any point, it should be DMA_BIDIRECTIONAL (see may write to it at any point, it should be DMA_BIDIRECTIONAL (see
below). below).
DMA_FROM_DEVICE synchronisation must be done before the driver DMA_FROM_DEVICE synchronisation must be done before the driver
accesses data that may be changed by the device. This memory should accesses data that may be changed by the device. This memory should
be treated as read only by the driver. If the driver needs to write be treated as read-only by the driver. If the driver needs to write
to it at any point, it should be DMA_BIDIRECTIONAL (see below). to it at any point, it should be DMA_BIDIRECTIONAL (see below).
DMA_BIDIRECTIONAL requires special handling: it means that the driver DMA_BIDIRECTIONAL requires special handling: it means that the driver
@ -261,7 +261,7 @@ you must always sync bidirectional memory twice: once before the
memory is handed off to the device (to make sure all memory changes memory is handed off to the device (to make sure all memory changes
are flushed from the processor) and once before the data may be are flushed from the processor) and once before the data may be
accessed after being used by the device (to make sure any processor accessed after being used by the device (to make sure any processor
cache lines are updated with data that the device may have changed. cache lines are updated with data that the device may have changed).
void void
dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size, dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size,
@ -302,8 +302,8 @@ pci_dma_mapping_error(dma_addr_t dma_addr)
In some circumstances dma_map_single and dma_map_page will fail to create In some circumstances dma_map_single and dma_map_page will fail to create
a mapping. A driver can check for these errors by testing the returned a mapping. A driver can check for these errors by testing the returned
dma address with dma_mapping_error(). A non zero return value means the mapping dma address with dma_mapping_error(). A non-zero return value means the mapping
could not be created and the driver should take appropriate action (eg could not be created and the driver should take appropriate action (e.g.
reduce current DMA mapping usage or delay and try again later). reduce current DMA mapping usage or delay and try again later).
int int
@ -315,7 +315,7 @@ reduce current DMA mapping usage or delay and try again later).
Maps a scatter gather list from the block layer. Maps a scatter gather list from the block layer.
Returns: the number of physical segments mapped (this may be shorted Returns: the number of physical segments mapped (this may be shorter
than <nents> passed in if the block layer determines that some than <nents> passed in if the block layer determines that some
elements of the scatter/gather list are physically adjacent and thus elements of the scatter/gather list are physically adjacent and thus
may be mapped with a single entry). may be mapped with a single entry).
@ -357,7 +357,7 @@ accessed sg->address and sg->length as shown above.
pci_unmap_sg(struct pci_dev *hwdev, struct scatterlist *sg, pci_unmap_sg(struct pci_dev *hwdev, struct scatterlist *sg,
int nents, int direction) int nents, int direction)
unmap the previously mapped scatter/gather list. All the parameters Unmap the previously mapped scatter/gather list. All the parameters
must be the same as those and passed in to the scatter/gather mapping must be the same as those and passed in to the scatter/gather mapping
API. API.
@ -377,7 +377,7 @@ void
pci_dma_sync_sg(struct pci_dev *hwdev, struct scatterlist *sg, pci_dma_sync_sg(struct pci_dev *hwdev, struct scatterlist *sg,
int nelems, int direction) int nelems, int direction)
synchronise a single contiguous or scatter/gather mapping. All the Synchronise a single contiguous or scatter/gather mapping. All the
parameters must be the same as those passed into the single mapping parameters must be the same as those passed into the single mapping
API. API.
@ -406,7 +406,7 @@ API at all.
void * void *
dma_alloc_noncoherent(struct device *dev, size_t size, dma_alloc_noncoherent(struct device *dev, size_t size,
dma_addr_t *dma_handle, int flag) dma_addr_t *dma_handle, gfp_t flag)
Identical to dma_alloc_coherent() except that the platform will Identical to dma_alloc_coherent() except that the platform will
choose to return either consistent or non-consistent memory as it sees choose to return either consistent or non-consistent memory as it sees
@ -426,34 +426,34 @@ void
dma_free_noncoherent(struct device *dev, size_t size, void *cpu_addr, dma_free_noncoherent(struct device *dev, size_t size, void *cpu_addr,
dma_addr_t dma_handle) dma_addr_t dma_handle)
free memory allocated by the nonconsistent API. All parameters must Free memory allocated by the nonconsistent API. All parameters must
be identical to those passed in (and returned by be identical to those passed in (and returned by
dma_alloc_noncoherent()). dma_alloc_noncoherent()).
int int
dma_is_consistent(struct device *dev, dma_addr_t dma_handle) dma_is_consistent(struct device *dev, dma_addr_t dma_handle)
returns true if the device dev is performing consistent DMA on the memory Returns true if the device dev is performing consistent DMA on the memory
area pointed to by the dma_handle. area pointed to by the dma_handle.
int int
dma_get_cache_alignment(void) dma_get_cache_alignment(void)
returns the processor cache alignment. This is the absolute minimum Returns the processor cache alignment. This is the absolute minimum
alignment *and* width that you must observe when either mapping alignment *and* width that you must observe when either mapping
memory or doing partial flushes. memory or doing partial flushes.
Notes: This API may return a number *larger* than the actual cache 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 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 into the width returned by this call. It will also always be a power
of two for easy alignment of two for easy alignment.
void void
dma_sync_single_range(struct device *dev, dma_addr_t dma_handle, dma_sync_single_range(struct device *dev, dma_addr_t dma_handle,
unsigned long offset, size_t size, unsigned long offset, size_t size,
enum dma_data_direction direction) enum dma_data_direction direction)
does a partial sync. starting at offset and continuing for size. You Does a partial sync, starting at offset and continuing for size. You
must be careful to observe the cache alignment and width when doing must be careful to observe the cache alignment and width when doing
anything like this. You must also be extra careful about accessing anything like this. You must also be extra careful about accessing
memory you intend to sync partially. memory you intend to sync partially.
@ -472,21 +472,20 @@ dma_declare_coherent_memory(struct device *dev, dma_addr_t bus_addr,
dma_addr_t device_addr, size_t size, int dma_addr_t device_addr, size_t size, int
flags) flags)
Declare region of memory to be handed out by dma_alloc_coherent when Declare region of memory to be handed out by dma_alloc_coherent when
it's asked for coherent memory for this device. it's asked for coherent memory for this device.
bus_addr is the physical address to which the memory is currently bus_addr is the physical address to which the memory is currently
assigned in the bus responding region (this will be used by the assigned in the bus responding region (this will be used by the
platform to perform the mapping) platform to perform the mapping).
device_addr is the physical address the device needs to be programmed device_addr is the physical address the device needs to be programmed
with actually to address this memory (this will be handed out as the with actually to address this memory (this will be handed out as the
dma_addr_t in dma_alloc_coherent()) dma_addr_t in dma_alloc_coherent()).
size is the size of the area (must be multiples of PAGE_SIZE). size is the size of the area (must be multiples of PAGE_SIZE).
flags can be or'd together and are flags can be or'd together and are:
DMA_MEMORY_MAP - request that the memory returned from DMA_MEMORY_MAP - request that the memory returned from
dma_alloc_coherent() be directly writable. dma_alloc_coherent() be directly writable.
@ -494,7 +493,7 @@ dma_alloc_coherent() be directly writable.
DMA_MEMORY_IO - request that the memory returned from DMA_MEMORY_IO - request that the memory returned from
dma_alloc_coherent() be addressable using read/write/memcpy_toio etc. dma_alloc_coherent() be addressable using read/write/memcpy_toio etc.
One or both of these flags must be present One or both of these flags must be present.
DMA_MEMORY_INCLUDES_CHILDREN - make the declared memory be allocated by DMA_MEMORY_INCLUDES_CHILDREN - make the declared memory be allocated by
dma_alloc_coherent of any child devices of this one (for memory residing dma_alloc_coherent of any child devices of this one (for memory residing
@ -528,7 +527,7 @@ dma_release_declared_memory(struct device *dev)
Remove the memory region previously declared from the system. This Remove the memory region previously declared from the system. This
API performs *no* in-use checking for this region and will return API performs *no* in-use checking for this region and will return
unconditionally having removed all the required structures. It is the unconditionally having removed all the required structures. It is the
drivers job to ensure that no parts of this memory region are driver's job to ensure that no parts of this memory region are
currently in use. currently in use.
void * void *
@ -538,12 +537,10 @@ dma_mark_declared_memory_occupied(struct device *dev,
This is used to occupy specific regions of the declared space This is used to occupy specific regions of the declared space
(dma_alloc_coherent() will hand out the first free region it finds). (dma_alloc_coherent() will hand out the first free region it finds).
device_addr is the *device* address of the region requested device_addr is the *device* address of the region requested.
size is the size (and should be a page sized multiple). size is the size (and should be a page-sized multiple).
The return value will be either a pointer to the processor virtual The return value will be either a pointer to the processor virtual
address of the memory, or an error (via PTR_ERR()) if any part of the address of the memory, or an error (via PTR_ERR()) if any part of the
region is occupied. region is occupied.