Skip to content

L
linux-davinci
Commit f5a69f4c authored by FUJITA Tomonori's avatar FUJITA Tomonori Committed by Linus Torvalds
Browse files
Options

Documentation: remove the PCI DMA API description in DMA-API.txt 

- remove the PCI DMA API description in DMA-API.txt
- remove the descriptions of dma_unmap macros since
  PCI-DMA-mapping.txt has the same description.
Signed-off-by: default avatarFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: "David S. Miller" <davem@davemloft.net>
Reviewed-by: default avatarRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 216bf58f
Hide whitespace changes
Inline Side-by-side
Showing with 15 additions and 137 deletions
Documentation/DMA-API.txt
View file @ f5a69f4c
......@@ -4,20 +4,18 @@
James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
This document describes the DMA API. For a more gentle introduction
phrased in terms of the pci_ equivalents (and actual examples) see
of the API (and actual examples) see
Documentation/PCI/PCI-DMA-mapping.txt.
This API is split into two pieces. Part I describes the API and the
corresponding pci_ API. Part II describes the extensions to the API
for supporting non-consistent memory machines. Unless you know that
your driver absolutely has to support non-consistent platforms (this
is usually only legacy platforms) you should only use the API
described in part I.
This API is split into two pieces. Part I describes the API. Part II
describes the extensions to the API for supporting non-consistent
memory machines. Unless you know that your driver absolutely has to
support non-consistent platforms (this is usually only legacy
platforms) you should only use the API described in part I.
Part I - pci_ and dma_ Equivalent API
Part I - dma_ API
-------------------------------------
To get the pci_ API, you must #include <linux/pci.h>
To get the dma_ API, you must #include <linux/dma-mapping.h>
......@@ -27,9 +25,6 @@ Part Ia - Using large dma-coherent buffers
void *
dma_alloc_coherent(struct device *dev, size_t size,
dma_addr_t *dma_handle, gfp_t flag)
void *
pci_alloc_consistent(struct pci_dev *dev, size_t size,
dma_addr_t *dma_handle)
Consistent memory is memory for which a write by either the device or
the processor can immediately be read by the processor or device
......@@ -53,15 +48,11 @@ 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
specify the GFP_ flags (see kmalloc) for the allocation (the
implementation may choose to ignore flags that affect the location of
the returned memory, like GFP_DMA). For pci_alloc_consistent, you
must assume GFP_ATOMIC behaviour.
the returned memory, like GFP_DMA).
void
dma_free_coherent(struct device *dev, size_t size, void *cpu_addr,
dma_addr_t dma_handle)
void
pci_free_consistent(struct pci_dev *dev, size_t size, void *cpu_addr,
dma_addr_t dma_handle)
Free the region of consistent memory you previously allocated. dev,
size and dma_handle must all be the same as those passed into the
......@@ -89,10 +80,6 @@ for alignment, like queue heads needing to be aligned on N-byte boundaries.
dma_pool_create(const char *name, struct device *dev,
size_t size, size_t align, size_t alloc);
struct pci_pool *
pci_pool_create(const char *name, struct pci_device *dev,
size_t size, size_t align, size_t alloc);
The pool create() routines initialize a pool of dma-coherent buffers
for use with a given device. It must be called in a context which
can sleep.
......@@ -108,9 +95,6 @@ from this pool must not cross 4KByte boundaries.
void *dma_pool_alloc(struct dma_pool *pool, gfp_t gfp_flags,
dma_addr_t *dma_handle);
void *pci_pool_alloc(struct pci_pool *pool, gfp_t gfp_flags,
dma_addr_t *dma_handle);
This allocates memory from the pool; the returned memory will meet the size
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),
......@@ -122,9 +106,6 @@ pool's device.
void dma_pool_free(struct dma_pool *pool, void *vaddr,
dma_addr_t addr);
void pci_pool_free(struct pci_pool *pool, void *vaddr,
dma_addr_t addr);
This puts memory back into the pool. The pool is what was passed to
the pool allocation routine; the cpu (vaddr) and dma addresses are what
were returned when that routine allocated the memory being freed.
......@@ -132,8 +113,6 @@ were returned when that routine allocated the memory being freed.
void dma_pool_destroy(struct dma_pool *pool);
void pci_pool_destroy(struct pci_pool *pool);
The pool destroy() routines free the resources of the pool. They must be
called in a context which can sleep. Make sure you've freed all allocated
memory back to the pool before you destroy it.
......@@ -144,8 +123,6 @@ Part Ic - DMA addressing limitations
int
dma_supported(struct device *dev, u64 mask)
int
pci_dma_supported(struct pci_dev *hwdev, u64 mask)
Checks to see if the device can support DMA to the memory described by
mask.
......@@ -159,8 +136,6 @@ driver writers.
int
dma_set_mask(struct device *dev, u64 mask)
int
pci_set_dma_mask(struct pci_device *dev, u64 mask)
Checks to see if the mask is possible and updates the device
parameters if it is.
......@@ -169,8 +144,6 @@ Returns: 0 if successful and a negative error if not.
int
dma_set_coherent_mask(struct device *dev, u64 mask)
int
pci_set_consistent_dma_mask(struct pci_device *dev, u64 mask)
Checks to see if the mask is possible and updates the device
parameters if it is.
......@@ -197,9 +170,6 @@ Part Id - Streaming DMA mappings
dma_addr_t
dma_map_single(struct device *dev, void *cpu_addr, size_t size,
enum dma_data_direction direction)
dma_addr_t
pci_map_single(struct pci_dev *hwdev, void *cpu_addr, size_t size,
int direction)
Maps a piece of processor virtual memory so it can be accessed by the
device and returns the physical handle of the memory.
......@@ -208,14 +178,10 @@ The direction for both api's may be converted freely by casting.
However the dma_ API uses a strongly typed enumerator for its
direction:
DMA_NONE = PCI_DMA_NONE no direction (used for
debugging)
DMA_TO_DEVICE = PCI_DMA_TODEVICE data is going from the
memory to the device
DMA_FROM_DEVICE = PCI_DMA_FROMDEVICE data is coming from
the device to the
memory
DMA_BIDIRECTIONAL = PCI_DMA_BIDIRECTIONAL direction isn't known
DMA_NONE no direction (used for debugging)
DMA_TO_DEVICE data is going from the memory to the device
DMA_FROM_DEVICE data is coming from the device to the memory
DMA_BIDIRECTIONAL direction isn't known
Notes: Not all memory regions in a machine can be mapped by this
API. Further, regions that appear to be physically contiguous in
......@@ -278,9 +244,6 @@ cache lines are updated with data that the device may have changed).
void
dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size,
enum dma_data_direction direction)
void
pci_unmap_single(struct pci_dev *hwdev, dma_addr_t dma_addr,
size_t size, int direction)
Unmaps the region previously mapped. All the parameters passed in
must be identical to those passed in (and returned) by the mapping
......@@ -290,15 +253,9 @@ dma_addr_t
dma_map_page(struct device *dev, struct page *page,
unsigned long offset, size_t size,
enum dma_data_direction direction)
dma_addr_t
pci_map_page(struct pci_dev *hwdev, struct page *page,
unsigned long offset, size_t size, int direction)
void
dma_unmap_page(struct device *dev, dma_addr_t dma_address, size_t size,
enum dma_data_direction direction)
void
pci_unmap_page(struct pci_dev *hwdev, dma_addr_t dma_address,
size_t size, int direction)
API for mapping and unmapping for pages. All the notes and warnings
for the other mapping APIs apply here. Also, although the <offset>
......@@ -309,9 +266,6 @@ cache width is.
int
dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
int
pci_dma_mapping_error(struct pci_dev *hwdev, dma_addr_t dma_addr)
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
dma address with dma_mapping_error(). A non-zero return value means the mapping
......@@ -321,9 +275,6 @@ reduce current DMA mapping usage or delay and try again later).
int
dma_map_sg(struct device *dev, struct scatterlist *sg,
int nents, enum dma_data_direction direction)
int
pci_map_sg(struct pci_dev *hwdev, struct scatterlist *sg,
int nents, int direction)
Returns: the number of physical segments mapped (this may be shorter
than <nents> passed in if some elements of the scatter/gather list are
......@@ -363,9 +314,6 @@ accessed sg->address and sg->length as shown above.
void
dma_unmap_sg(struct device *dev, struct scatterlist *sg,
int nhwentries, enum dma_data_direction direction)
void
pci_unmap_sg(struct pci_dev *hwdev, struct scatterlist *sg,
int nents, int direction)
Unmap the previously mapped scatter/gather list. All the parameters
must be the same as those and passed in to the scatter/gather mapping
......@@ -378,26 +326,14 @@ void
dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle, size_t size,
enum dma_data_direction direction)
void
pci_dma_sync_single_for_cpu(struct pci_dev *hwdev, dma_addr_t dma_handle,
size_t size, int direction)
void
dma_sync_single_for_device(struct device *dev, dma_addr_t dma_handle, size_t size,
enum dma_data_direction direction)
void
pci_dma_sync_single_for_device(struct pci_dev *hwdev, dma_addr_t dma_handle,
size_t size, int direction)
void
dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, int nelems,
enum dma_data_direction direction)
void
pci_dma_sync_sg_for_cpu(struct pci_dev *hwdev, struct scatterlist *sg,
int nelems, int direction)
void
dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, int nelems,
enum dma_data_direction direction)
void
pci_dma_sync_sg_for_device(struct pci_dev *hwdev, struct scatterlist *sg,
int nelems, int 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
......@@ -482,70 +418,12 @@ void whizco_dma_map_sg_attrs(struct device *dev, dma_addr_t dma_addr,
....
Part Ie - Optimizing Unmap State Space Consumption
--------------------------------
On some platforms, dma_unmap_{single,page}() is simply a nop.
Therefore, keeping track of the mapping address and length is a waste
of space. Instead of filling your drivers up with ifdefs and the like
to "work around" this (which would defeat the whole purpose of a
portable API) the following facilities are provided.
Actually, instead of describing the macros one by one, we'll
transform some example code.
1) Use DEFINE_DMA_UNMAP_{ADDR,LEN} in state saving structures.
Example, before:
struct ring_state {
struct sk_buff *skb;
dma_addr_t mapping;
__u32 len;
};
after:
struct ring_state {
struct sk_buff *skb;
DEFINE_DMA_UNMAP_ADDR(mapping);
DEFINE_DMA_UNMAP_LEN(len);
};
2) Use dma_unmap_{addr,len}_set to set these values.
Example, before:
ringp->mapping = FOO;
ringp->len = BAR;
after:
dma_unmap_addr_set(ringp, mapping, FOO);
dma_unmap_len_set(ringp, len, BAR);
3) Use dma_unmap_{addr,len} to access these values.
Example, before:
dma_unmap_single(dev, ringp->mapping, ringp->len,
DMA_FROM_DEVICE);
after:
dma_unmap_single(dev,
dma_unmap_addr(ringp, mapping),
dma_unmap_len(ringp, len),
DMA_FROM_DEVICE);
It really should be self-explanatory. We treat the ADDR and LEN
separately, because it is possible for an implementation to only
need the address in order to perform the unmap operation.
Part II - Advanced dma_ usage
-----------------------------
Warning: These pieces of the DMA API have no PCI equivalent. They
should also not be used in the majority of cases, since they cater for
unlikely corner cases that don't belong in usual drivers.
Warning: These pieces of the DMA API should not be used in the
majority of cases, since they cater for unlikely corner cases that
don't belong in usual drivers.
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
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment