linux-kernel - [patch V3 21/37] Documentation/io-mapping: Remove outdated blurb

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Message-Id: <20201103095858.734064977@linutronix.de>
Date:   Tue, 03 Nov 2020 10:27:33 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
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Subject: [patch V3 21/37] Documentation/io-mapping: Remove outdated blurb

The implementation details in the documentation are outdated and not really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@...utronix.de>
---
V3: New patch
---
 Documentation/driver-api/io-mapping.rst |   22 ----------------------
 1 file changed, 22 deletions(-)

--- 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.