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authorMauro Carvalho Chehab <mchehab@s-opensource.com>2017-05-14 14:32:35 -0300
committerJonathan Corbet <corbet@lwn.net>2017-07-14 13:51:38 -0600
commit9cf5116d5b10793b5105f962fa3d899b2d6cb5f6 (patch)
treedfb38c3b07c8292c3f7da2dfe0c83c44e0859a80 /Documentation/io-mapping.txt
parent45d85146269f711b8fbfdda017a033676caf29ab (diff)
downloadlinux-stericsson-9cf5116d5b10793b5105f962fa3d899b2d6cb5f6.tar.gz
io-mapping.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: - Add a title for the document and for API chapter; - mark literal blocks; - Adjust whitespacing. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/io-mapping.txt')
-rw-r--r--Documentation/io-mapping.txt67
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