[V3,21/37] Documentation/io-mapping: Remove outdated blurb
diff mbox series

Message ID 20201103095858.734064977@linutronix.de
State New, archived
Headers show
Series
  • mm/highmem: Preemptible variant of kmap_atomic & friends
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Commit Message

Thomas Gleixner Nov. 3, 2020, 9:27 a.m. UTC
The implementation details in the documentation are outdated and not really
helpful. Remove them.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V3: New patch
---
 Documentation/driver-api/io-mapping.rst |   22 ----------------------
 1 file changed, 22 deletions(-)

Patch
diff mbox series

--- 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.