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authorMauro Carvalho Chehab <mchehab@s-opensource.com>2017-05-14 10:27:52 (GMT)
committerJonathan Corbet <corbet@lwn.net>2017-07-14 19:51:32 (GMT)
commit03158a70adde2fd46b0f266b5d1090efe2ff6887 (patch)
tree8390b5182d58f22cb460f2f27981f93faaa01d47 /Documentation/DMA-API.txt
parenta2fbbcea7bb9b1b6d29a24b1e74a6cffd6dd44e6 (diff)
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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>
Diffstat (limited to 'Documentation/DMA-API.txt')
-rw-r--r--Documentation/DMA-API.txt580
1 files changed, 329 insertions, 251 deletions
diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index 71200df..45b2932 100644
--- a/Documentation/DMA-API.txt
+++ b/Documentation/DMA-API.txt
@@ -1,7 +1,8 @@
- Dynamic DMA mapping using the generic device
- ============================================
+============================================
+Dynamic DMA mapping using the generic device
+============================================
- James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
+:Author: James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
This document describes the DMA API. For a more gentle introduction
of the API (and actual examples), see Documentation/DMA-API-HOWTO.txt.
@@ -12,10 +13,10 @@ 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 - dma_ API
--------------------------------------
+Part I - dma_API
+----------------
-To get the dma_ API, you must #include <linux/dma-mapping.h>. This
+To get the dma_API, you must #include <linux/dma-mapping.h>. This
provides dma_addr_t and the interfaces described below.
A dma_addr_t can hold any valid DMA address for the platform. It can be
@@ -26,9 +27,11 @@ address space and the DMA address space.
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 *
+ dma_alloc_coherent(struct device *dev, size_t size,
+ dma_addr_t *dma_handle, gfp_t flag)
Consistent memory is memory for which a write by either the device or
the processor can immediately be read by the processor or device
@@ -51,20 +54,24 @@ consolidate your requests for consistent memory as much as possible.
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
+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).
-void *
-dma_zalloc_coherent(struct device *dev, size_t size,
- dma_addr_t *dma_handle, gfp_t flag)
+::
+
+ void *
+ dma_zalloc_coherent(struct device *dev, size_t size,
+ dma_addr_t *dma_handle, gfp_t flag)
Wraps dma_alloc_coherent() and also zeroes the returned memory if the
allocation attempt succeeded.
-void
-dma_free_coherent(struct device *dev, size_t size, void *cpu_addr,
- dma_addr_t dma_handle)
+::
+
+ void
+ dma_free_coherent(struct device *dev, size_t size, void *cpu_addr,
+ dma_addr_t dma_handle)
Free a region of consistent memory you previously allocated. dev,
size and dma_handle must all be the same as those passed into
@@ -78,7 +85,7 @@ may only be called with IRQs enabled.
Part Ib - Using small DMA-coherent buffers
------------------------------------------
-To get this part of the dma_ API, you must #include <linux/dmapool.h>
+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
descriptors or I/O buffers. Rather than allocating in units of a page
@@ -88,6 +95,8 @@ not __get_free_pages(). Also, they understand common hardware constraints
for alignment, like queue heads needing to be aligned on N-byte boundaries.
+::
+
struct dma_pool *
dma_pool_create(const char *name, struct device *dev,
size_t size, size_t align, size_t alloc);
@@ -103,16 +112,21 @@ in bytes, and must be a power of two). If your device has no boundary
crossing restrictions, pass 0 for alloc; passing 4096 says memory allocated
from this pool must not cross 4KByte boundaries.
+::
- void *dma_pool_zalloc(struct dma_pool *pool, gfp_t mem_flags,
- dma_addr_t *handle)
+ void *
+ dma_pool_zalloc(struct dma_pool *pool, gfp_t mem_flags,
+ dma_addr_t *handle)
Wraps dma_pool_alloc() and also zeroes the returned memory if the
allocation attempt succeeded.
- void *dma_pool_alloc(struct dma_pool *pool, gfp_t gfp_flags,
- dma_addr_t *dma_handle);
+::
+
+ void *
+ dma_pool_alloc(struct dma_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
@@ -122,16 +136,20 @@ blocking. Like dma_alloc_coherent(), this returns two values: an
address usable by the CPU, and the DMA address usable by the pool's
device.
+::
- void dma_pool_free(struct dma_pool *pool, void *vaddr,
- dma_addr_t addr);
+ void
+ dma_pool_free(struct dma_pool *pool, void *vaddr,
+ dma_addr_t addr);
This puts memory back into the pool. The pool is what was passed to
dma_pool_alloc(); 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
+ dma_pool_destroy(struct dma_pool *pool);
dma_pool_destroy() frees the resources of the pool. It must be
called in a context which can sleep. Make sure you've freed all allocated
@@ -141,32 +159,40 @@ memory back to the pool before you destroy it.
Part Ic - DMA addressing limitations
------------------------------------
-int
-dma_set_mask_and_coherent(struct device *dev, u64 mask)
+::
+
+ int
+ dma_set_mask_and_coherent(struct device *dev, u64 mask)
Checks to see if the mask is possible and updates the device
streaming and coherent DMA mask parameters if it is.
Returns: 0 if successful and a negative error if not.
-int
-dma_set_mask(struct device *dev, u64 mask)
+::
+
+ int
+ dma_set_mask(struct device *dev, u64 mask)
Checks to see if the mask is possible and updates the device
parameters if it is.
Returns: 0 if successful and a negative error if not.
-int
-dma_set_coherent_mask(struct device *dev, u64 mask)
+::
+
+ int
+ dma_set_coherent_mask(struct device *dev, u64 mask)
Checks to see if the mask is possible and updates the device
parameters if it is.
Returns: 0 if successful and a negative error if not.
-u64
-dma_get_required_mask(struct device *dev)
+::
+
+ u64
+ dma_get_required_mask(struct device *dev)
This API returns the mask that the platform requires to
operate efficiently. Usually this means the returned mask
@@ -182,94 +208,107 @@ call to set the mask to the value returned.
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
+ dma_map_single(struct device *dev, void *cpu_addr, size_t size,
+ enum dma_data_direction direction)
Maps a piece of processor virtual memory so it can be accessed by the
device and returns the DMA address of the memory.
The direction for both APIs may be converted freely by casting.
-However the dma_ API uses a strongly typed enumerator for its
+However the dma_API uses a strongly typed enumerator for its
direction:
+======================= =============================================
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
+======================= =============================================
+
+.. note::
+
+ Not all memory regions in a machine can be mapped by this API.
+ Further, contiguous kernel virtual space may not be contiguous as
+ physical memory. Since 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. For this reason, memory to be mapped by
+ this API should be obtained from sources which guarantee it to be
+ physically contiguous (like kmalloc).
+
+ Further, the DMA address of the memory must be within the
+ dma_mask of the device (the dma_mask is a bit mask of the
+ addressable region for the device, i.e., if the DMA address of
+ the memory ANDed with the dma_mask is still equal to the DMA
+ address, then the device can perform DMA to the memory). To
+ ensure that the memory allocated by kmalloc is within the dma_mask,
+ the driver may specify various platform-dependent flags to restrict
+ the DMA address range of the allocation (e.g., on x86, GFP_DMA
+ guarantees to be within the first 16MB of available DMA addresses,
+ as required by ISA devices).
+
+ Note also that the above constraints on physical contiguity and
+ dma_mask may not apply if the platform has an IOMMU (a device which
+ maps an I/O DMA address to a physical memory address). However, to be
+ portable, device driver writers may *not* assume that such an IOMMU
+ exists.
+
+.. warning::
+
+ Memory coherency operates at a granularity called the cache
+ line width. In order for memory mapped by this API to operate
+ correctly, the mapped region must begin exactly on a cache line
+ boundary and end exactly on one (to prevent two separately mapped
+ regions from sharing a single cache line). Since the cache line size
+ may not be known at compile time, the API will not enforce this
+ requirement. Therefore, it is recommended that driver writers who
+ don't take special care to determine the cache line size at run time
+ only map virtual regions that begin and end on page boundaries (which
+ are guaranteed also to be cache line boundaries).
+
+ 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
+ the device. Once this primitive is used, memory covered by this
+ 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
+ below).
+
+ DMA_FROM_DEVICE synchronisation must be done before the driver
+ 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
+ to it at any point, it should be DMA_BIDIRECTIONAL (see below).
+
+ DMA_BIDIRECTIONAL requires special handling: it means that the driver
+ isn't sure if the memory was modified before being handed off to the
+ device and also isn't sure if the device will also modify it. Thus,
+ you must always sync bidirectional memory twice: once before the
+ 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
+ accessed after being used by the device (to make sure any processor
+ cache lines are updated with data that the device may have changed).
+
+::
-Notes: Not all memory regions in a machine can be mapped by this API.
-Further, contiguous kernel virtual space may not be contiguous as
-physical memory. Since 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. For this reason, memory to be mapped by
-this API should be obtained from sources which guarantee it to be
-physically contiguous (like kmalloc).
-
-Further, the DMA address of the memory must be within the
-dma_mask of the device (the dma_mask is a bit mask of the
-addressable region for the device, i.e., if the DMA address of
-the memory ANDed with the dma_mask is still equal to the DMA
-address, then the device can perform DMA to the memory). To
-ensure that the memory allocated by kmalloc is within the dma_mask,
-the driver may specify various platform-dependent flags to restrict
-the DMA address range of the allocation (e.g., on x86, GFP_DMA
-guarantees to be within the first 16MB of available DMA addresses,
-as required by ISA devices).
-
-Note also that the above constraints on physical contiguity and
-dma_mask may not apply if the platform has an IOMMU (a device which
-maps an I/O DMA address to a physical memory address). However, to be
-portable, device driver writers may *not* assume that such an IOMMU
-exists.
-
-Warnings: Memory coherency operates at a granularity called the cache
-line width. In order for memory mapped by this API to operate
-correctly, the mapped region must begin exactly on a cache line
-boundary and end exactly on one (to prevent two separately mapped
-regions from sharing a single cache line). Since the cache line size
-may not be known at compile time, the API will not enforce this
-requirement. Therefore, it is recommended that driver writers who
-don't take special care to determine the cache line size at run time
-only map virtual regions that begin and end on page boundaries (which
-are guaranteed also to be cache line boundaries).
-
-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
-the device. Once this primitive is used, memory covered by this
-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
-below).
-
-DMA_FROM_DEVICE synchronisation must be done before the driver
-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
-to it at any point, it should be DMA_BIDIRECTIONAL (see below).
-
-DMA_BIDIRECTIONAL requires special handling: it means that the driver
-isn't sure if the memory was modified before being handed off to the
-device and also isn't sure if the device will also modify it. Thus,
-you must always sync bidirectional memory twice: once before the
-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
-accessed after being used by the device (to make sure any processor
-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
+ dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size,
+ enum dma_data_direction direction)
Unmaps the region previously mapped. All the parameters passed in
must be identical to those passed in (and returned) by the mapping
API.
-dma_addr_t
-dma_map_page(struct device *dev, struct page *page,
- unsigned long offset, size_t size,
- enum dma_data_direction direction)
-void
-dma_unmap_page(struct device *dev, dma_addr_t dma_address, size_t size,
- enum dma_data_direction direction)
+::
+
+ dma_addr_t
+ dma_map_page(struct device *dev, struct page *page,
+ unsigned long offset, size_t size,
+ enum dma_data_direction direction)
+
+ void
+ dma_unmap_page(struct device *dev, dma_addr_t dma_address, size_t size,
+ enum dma_data_direction direction)
API for mapping and unmapping for pages. All the notes and warnings
for the other mapping APIs apply here. Also, although the <offset>
@@ -277,20 +316,24 @@ and <size> parameters are provided to do partial page mapping, it is
recommended that you never use these unless you really know what the
cache width is.
-dma_addr_t
-dma_map_resource(struct device *dev, phys_addr_t phys_addr, size_t size,
- enum dma_data_direction dir, unsigned long attrs)
+::
-void
-dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size,
- enum dma_data_direction dir, unsigned long attrs)
+ dma_addr_t
+ dma_map_resource(struct device *dev, phys_addr_t phys_addr, size_t size,
+ enum dma_data_direction dir, unsigned long attrs)
+
+ void
+ dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size,
+ enum dma_data_direction dir, unsigned long attrs)
API for mapping and unmapping for MMIO resources. All the notes and
warnings for the other mapping APIs apply here. The API should only be
used to map device MMIO resources, mapping of RAM is not permitted.
-int
-dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
+::
+
+ int
+ dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
In some circumstances dma_map_single(), dma_map_page() and dma_map_resource()
will fail to create a mapping. A driver can check for these errors by testing
@@ -298,9 +341,11 @@ the returned 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 (e.g. 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 nents, enum dma_data_direction direction)
Returns: the number of DMA address segments mapped (this may be shorter
than <nents> passed in if some elements of the scatter/gather list are
@@ -316,7 +361,7 @@ critical that the driver do something, in the case of a block driver
aborting the request or even oopsing is better than doing nothing and
corrupting the filesystem.
-With scatterlists, you use the resulting mapping like this:
+With scatterlists, you use the resulting mapping like this::
int i, count = dma_map_sg(dev, sglist, nents, direction);
struct scatterlist *sg;
@@ -337,9 +382,11 @@ Then you should loop count times (note: this can be less than nents times)
and use sg_dma_address() and sg_dma_len() macros where you previously
accessed sg->address and sg->length as shown above.
+::
+
void
dma_unmap_sg(struct device *dev, struct scatterlist *sg,
- int nents, enum dma_data_direction direction)
+ int nents, enum dma_data_direction 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
@@ -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)
+::
+
+ 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)
+ void
+ dma_unmap_single_attrs(struct device *dev, dma_addr_t dma_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)
+ 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)
+ 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.:
-
-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 */
- ....
+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 */
+ ....
+ }
-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:
-
-------------[ 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 ]---
+example warning message may look like this::
+
+ WARNING: at /data2/repos/linux-2.6-iommu/lib/dma-debug.c:448
+ check_unmap+0x203/0x490()
+ Hardware name:
+ forcedeth 0000:00:08.0: DMA-API: device driver frees DMA memory with wrong
+ function [device address=0x00000000640444be] [size=66 bytes] [mapped as
+ single] [unmapped as page]
+ Modules linked in: nfsd exportfs bridge stp llc r8169
+ Pid: 0, comm: swapper Tainted: G W 2.6.28-dmatest-09289-g8bb99c0 #1
+ Call Trace:
+ <IRQ> [<ffffffff80240b22>] warn_slowpath+0xf2/0x130
+ [<ffffffff80647b70>] _spin_unlock+0x10/0x30
+ [<ffffffff80537e75>] usb_hcd_link_urb_to_ep+0x75/0xc0
+ [<ffffffff80647c22>] _spin_unlock_irqrestore+0x12/0x40
+ [<ffffffff8055347f>] ohci_urb_enqueue+0x19f/0x7c0
+ [<ffffffff80252f96>] queue_work+0x56/0x60
+ [<ffffffff80237e10>] enqueue_task_fair+0x20/0x50
+ [<ffffffff80539279>] usb_hcd_submit_urb+0x379/0xbc0
+ [<ffffffff803b78c3>] cpumask_next_and+0x23/0x40
+ [<ffffffff80235177>] find_busiest_group+0x207/0x8a0
+ [<ffffffff8064784f>] _spin_lock_irqsave+0x1f/0x50
+ [<ffffffff803c7ea3>] check_unmap+0x203/0x490
+ [<ffffffff803c8259>] debug_dma_unmap_page+0x49/0x50
+ [<ffffffff80485f26>] nv_tx_done_optimized+0xc6/0x2c0
+ [<ffffffff80486c13>] nv_nic_irq_optimized+0x73/0x2b0
+ [<ffffffff8026df84>] handle_IRQ_event+0x34/0x70
+ [<ffffffff8026ffe9>] handle_edge_irq+0xc9/0x150
+ [<ffffffff8020e3ab>] do_IRQ+0xcb/0x1c0
+ [<ffffffff8020c093>] ret_from_intr+0x0/0xa
+ <EOI> <4>---[ end trace f6435a98e2a38c0e ]---
The driver developer can find the driver and the device including a stacktrace
of the DMA-API call which caused this warning.
@@ -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.
-