[tip: core/mm] Documentation/io-mapping: Remove outdated blurb

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the core/mm branch of tip:

Commit-ID:     9bf6f7bab3bad4b30f108fca25aa5297dff0973f
Gitweb:        https://git.kernel.org/tip/9bf6f7bab3bad4b30f108fca25aa5297dff0973f
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Tue, 03 Nov 2020 10:27:33 +01:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Fri, 06 Nov 2020 23:14:58 +01:00

Documentation/io-mapping: Remove outdated blurb

The implementation details in the documentation are outdated and not really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@xxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20201103095858.734064977@xxxxxxxxxxxxx

---
 Documentation/driver-api/io-mapping.rst | 22 ----------------------
 1 file changed, 22 deletions(-)

diff --git a/Documentation/driver-api/io-mapping.rst b/Documentation/driver-api/io-mapping.rst
index a966239..e33b882 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.