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author | Linus Torvalds <torvalds@linux-foundation.org> | 2017-07-15 22:58:58 +0300 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-07-15 22:58:58 +0300 |
commit | 486088bc4689f826b80aa317b45ac9e42e8b25ee (patch) | |
tree | adf5847a6119d24da990d9e336f005c4a316e6be /Documentation/io-mapping.txt | |
parent | 52f6c588c77b76d548201470c2a28263a41b462b (diff) | |
parent | 43e5f7e1fa66531777c49791014c3124ea9208d8 (diff) | |
download | linux-486088bc4689f826b80aa317b45ac9e42e8b25ee.tar.xz |
Merge tag 'standardize-docs' of git://git.lwn.net/linux
Pull documentation format standardization from Jonathan Corbet:
"This series converts a number of top-level documents to the RST format
without incorporating them into the Sphinx tree. The hope is to bring
some uniformity to kernel documentation and, perhaps more importantly,
have our existing docs serve as an example of the desired formatting
for those that will be added later.
Mauro has gone through and fixed up a lot of top-level documentation
files to make them conform to the RST format, but without moving or
renaming them in any way. This will help when we incorporate the ones
we want to keep into the Sphinx doctree, but the real purpose is to
bring a bit of uniformity to our documentation and let the top-level
docs serve as examples for those writing new ones"
* tag 'standardize-docs' of git://git.lwn.net/linux: (84 commits)
docs: kprobes.txt: Fix whitespacing
tee.txt: standardize document format
cgroup-v2.txt: standardize document format
dell_rbu.txt: standardize document format
zorro.txt: standardize document format
xz.txt: standardize document format
xillybus.txt: standardize document format
vfio.txt: standardize document format
vfio-mediated-device.txt: standardize document format
unaligned-memory-access.txt: standardize document format
this_cpu_ops.txt: standardize document format
svga.txt: standardize document format
static-keys.txt: standardize document format
smsc_ece1099.txt: standardize document format
SM501.txt: standardize document format
siphash.txt: standardize document format
sgi-ioc4.txt: standardize document format
SAK.txt: standardize document format
rpmsg.txt: standardize document format
robust-futexes.txt: standardize document format
...
Diffstat (limited to 'Documentation/io-mapping.txt')
-rw-r--r-- | Documentation/io-mapping.txt | 67 |
1 files changed, 41 insertions, 26 deletions
diff --git a/Documentation/io-mapping.txt b/Documentation/io-mapping.txt index 5ca78426f54c..a966239f04e4 100644 --- a/Documentation/io-mapping.txt +++ b/Documentation/io-mapping.txt @@ -1,66 +1,81 @@ +======================== +The io_mapping functions +======================== + +API +=== + The io_mapping functions in linux/io-mapping.h provide an abstraction for efficiently mapping small regions of an I/O device to the CPU. The initial usage is to support the large graphics aperture on 32-bit processors where ioremap_wc cannot be used to statically map the entire aperture to the CPU as it would consume too much of the kernel address space. -A mapping object is created during driver initialization using +A mapping object is created during driver initialization using:: struct io_mapping *io_mapping_create_wc(unsigned long base, unsigned long size) - 'base' is the bus address of the region to be made - mappable, while 'size' indicates how large a mapping region to - enable. Both are in bytes. +'base' is the bus address of the region to be made +mappable, while 'size' indicates how large a mapping region to +enable. Both are in bytes. - This _wc variant provides a mapping which may only be used - with the io_mapping_map_atomic_wc or io_mapping_map_wc. +This _wc variant provides a mapping which may only be used +with the io_mapping_map_atomic_wc or io_mapping_map_wc. With this mapping object, individual pages can be mapped either atomically or not, depending on the necessary scheduling environment. Of course, atomic -maps are more efficient: +maps are more efficient:: void *io_mapping_map_atomic_wc(struct io_mapping *mapping, unsigned long offset) - 'offset' is the offset within the defined mapping region. - Accessing addresses beyond the region specified in the - creation function yields undefined results. Using an offset - which is not page aligned yields an undefined result. The - return value points to a single page in CPU address space. +'offset' is the offset within the defined mapping region. +Accessing addresses beyond the region specified in the +creation function yields undefined results. Using an offset +which is not page aligned yields an undefined result. The +return value points to a single page in CPU address space. + +This _wc variant returns a write-combining map to the +page and may only be used with mappings created by +io_mapping_create_wc - This _wc variant returns a write-combining map to the - page and may only be used with mappings created by - io_mapping_create_wc +Note that the task may not sleep while holding this page +mapped. - Note that the task may not sleep while holding this page - mapped. +:: void io_mapping_unmap_atomic(void *vaddr) - 'vaddr' must be the value returned by the last - io_mapping_map_atomic_wc call. This unmaps the specified - page and allows the task to sleep once again. +'vaddr' must be the value returned by the last +io_mapping_map_atomic_wc call. This unmaps the specified +page and allows the task to sleep once again. If you need to sleep while holding the lock, you can use the non-atomic variant, although they may be significantly slower. +:: + void *io_mapping_map_wc(struct io_mapping *mapping, unsigned long offset) - This works like io_mapping_map_atomic_wc except it allows - the task to sleep while holding the page mapped. +This works like io_mapping_map_atomic_wc except it allows +the task to sleep while holding the page mapped. + + +:: void io_mapping_unmap(void *vaddr) - This works like io_mapping_unmap_atomic, except it is used - for pages mapped with io_mapping_map_wc. +This works like io_mapping_unmap_atomic, except it is used +for pages mapped with io_mapping_map_wc. -At driver close time, the io_mapping object must be freed: +At driver close time, the io_mapping object must be freed:: void io_mapping_free(struct io_mapping *mapping) -Current Implementation: +Current Implementation +====================== The initial implementation of these functions uses existing mapping mechanisms and so provides only an abstraction layer and no new |