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Commit 9cf5116d authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab Committed by Jonathan Corbet
Browse files

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: default avatarMauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 45d85146

Documentation/io-mapping.txt

+41 −26
Original line number Diff line number Diff line 
========================

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)
@@ -18,7 +25,7 @@ A mapping object is created during driver initialization using 


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)
@@ -36,6 +43,8 @@ maps are more efficient: 
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
@@ -45,22 +54,28 @@ maps are more efficient: 
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.





::



	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.



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