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| author | Thomas Gleixner <tglx@linutronix.de> | 2020-11-03 12:27:33 +0300 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2020-11-07 01:14:58 +0300 |
| commit | 9bf6f7bab3bad4b30f108fca25aa5297dff0973f (patch) | |
| tree | d9879b8b4206244bdda88b5c787ef5a8421924e8 | |
| parent | 351191ad55c8a1eccaf23e4187c62056229c0779 (diff) | |
| download | linux-9bf6f7bab3bad4b30f108fca25aa5297dff0973f.tar.xz | |
Documentation/io-mapping: Remove outdated blurb
The implementation details in the documentation are outdated and not really
helpful. Remove them.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://lore.kernel.org/r/20201103095858.734064977@linutronix.de
| -rw-r--r-- | Documentation/driver-api/io-mapping.rst | 22 |
1 files changed, 0 insertions, 22 deletions
diff --git a/Documentation/driver-api/io-mapping.rst b/Documentation/driver-api/io-mapping.rst index a966239f04e4..e33b88268554 100644 --- a/Documentation/driver-api/io-mapping.rst +++ b/Documentation/driver-api/io-mapping.rst @@ -73,25 +73,3 @@ for pages mapped with io_mapping_map_wc. At driver close time, the io_mapping object must be freed:: void io_mapping_free(struct io_mapping *mapping) - -Current Implementation -====================== - -The initial implementation of these functions uses existing mapping -mechanisms and so provides only an abstraction layer and no new -functionality. - -On 64-bit processors, io_mapping_create_wc calls ioremap_wc for the whole -range, creating a permanent kernel-visible mapping to the resource. The -map_atomic and map functions add the requested offset to the base of the -virtual address returned by ioremap_wc. - -On 32-bit processors with HIGHMEM defined, io_mapping_map_atomic_wc uses -kmap_atomic_pfn to map the specified page in an atomic fashion; -kmap_atomic_pfn isn't really supposed to be used with device pages, but it -provides an efficient mapping for this usage. - -On 32-bit processors without HIGHMEM defined, io_mapping_map_atomic_wc and -io_mapping_map_wc both use ioremap_wc, a terribly inefficient function which -performs an IPI to inform all processors about the new mapping. This results -in a significant performance penalty. |