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authorThomas Gleixner <tglx@linutronix.de>2020-11-03 12:27:33 +0300
committerThomas Gleixner <tglx@linutronix.de>2020-11-07 01:14:58 +0300
commit9bf6f7bab3bad4b30f108fca25aa5297dff0973f (patch)
treed9879b8b4206244bdda88b5c787ef5a8421924e8 /Documentation/driver-api
parent351191ad55c8a1eccaf23e4187c62056229c0779 (diff)
downloadlinux-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Documentation/io-mapping: Remove outdated blurb
The implementation details in the documentation are outdated and not really helpful.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
Diffstat (limited to 'Documentation/driver-api')
-rw-r--r--Documentation/driver-api/io-mapping.rst22
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.