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yaml --- r: 118384 b: refs/heads/master c: 8d5c660 h: refs/heads/master v: v3
git-mirror · Nov 3, 2008 · 1a44da1 · 1a44da1
1 parent 1758958
commit 1a44da1
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Showing 2 changed files with 10 additions and 4 deletions.
diff --git a/[refs] b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 0839ccb8ac6a9e2d5e175a4ae9c82b5c574d510d
+refs/heads/master: 8d5c6603c408d91ecf543f244f10ccb8b500ad95
diff --git a/trunk/Documentation/io-mapping.txt b/trunk/Documentation/io-mapping.txt
@@ -71,6 +71,12 @@ 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, io_mapping_map_atomic_wc uses io_map_atomic_prot_pfn,
-which uses the fixmaps to get us a mapping to a page using an atomic fashion.
-For io_mapping_map_wc, ioremap_wc() is used to get a mapping of the region.
+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.