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>
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
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
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.
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),
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.
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.
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.
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.
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.
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.
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
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
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>
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
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
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
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
....
-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
projects / kernel.git / commitdiff