resources: add io-mapping functions to dynamically map large device apertures

Impact: add new generic io_map_*() APIs

Graphics devices have large PCI apertures which would consume a significant
fraction of a 32-bit address space if mapped during driver initialization.
Using ioremap at runtime is impractical as it is too slow.

This new set of interfaces uses atomic mappings on 32-bit processors and a
large static mapping on 64-bit processors to provide reasonable 32-bit
performance and optimal 64-bit performance.

The current implementation sits atop the io_map_atomic fixmap-based
mechanism for 32-bit processors.

This includes some editorial suggestions from Randy Dunlap for
Documentation/io-mapping.txt

Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Keith Packard 2008-10-30 19:38:18 -07:00 committed by Ingo Molnar
parent fd94093435
commit 9663f2e6a6
2 changed files with 194 additions and 0 deletions

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The io_mapping functions in linux/io-mapping.h provide an abstraction for
efficiently mapping small regions of an I/O device to the CPU. The initial
usage is to support the large graphics aperture on 32-bit processors where
ioremap_wc cannot be used to statically map the entire aperture to the CPU
as it would consume too much of the kernel address space.
A mapping object is created during driver initialization using
struct io_mapping *io_mapping_create_wc(unsigned long base,
unsigned long size)
'base' is the bus address of the region to be made
mappable, while 'size' indicates how large a mapping region to
enable. Both are in bytes.
This _wc variant provides a mapping which may only be used
with the io_mapping_map_atomic_wc or io_mapping_map_wc.
With this mapping object, individual pages can be mapped either atomically
or not, depending on the necessary scheduling environment. Of course, atomic
maps are more efficient:
void *io_mapping_map_atomic_wc(struct io_mapping *mapping,
unsigned long offset)
'offset' is the offset within the defined mapping region.
Accessing addresses beyond the region specified in the
creation function yields undefined results. Using an offset
which is not page aligned yields an undefined result. The
return value points to a single page in CPU address space.
This _wc variant returns a write-combining map to the
page and may only be used with mappings created by
io_mapping_create_wc
Note that the task may not sleep while holding this page
mapped.
void io_mapping_unmap_atomic(void *vaddr)
'vaddr' must be the the value returned by the last
io_mapping_map_atomic_wc call. This unmaps the specified
page and allows the task to sleep once again.
If you need to sleep while holding the lock, you can use the non-atomic
variant, although they may be significantly slower.
void *io_mapping_map_wc(struct io_mapping *mapping,
unsigned long offset)
This works like io_mapping_map_atomic_wc except it allows
the task to sleep while holding the page mapped.
void io_mapping_unmap(void *vaddr)
This works like io_mapping_unmap_atomic, except it is used
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, 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.

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include/linux/io-mapping.h Normal file
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/*
* Copyright © 2008 Keith Packard <keithp@keithp.com>
*
* This file is free software; you can redistribute it and/or modify
* it under the terms of version 2 of the GNU General Public License
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#ifndef _LINUX_IO_MAPPING_H
#define _LINUX_IO_MAPPING_H
#include <linux/types.h>
#include <asm/io.h>
#include <asm/page.h>
#include <asm/iomap.h>
/*
* The io_mapping mechanism provides an abstraction for mapping
* individual pages from an io device to the CPU in an efficient fashion.
*
* See Documentation/io_mapping.txt
*/
/* this struct isn't actually defined anywhere */
struct io_mapping;
#ifdef CONFIG_X86_64
/* Create the io_mapping object*/
static inline struct io_mapping *
io_mapping_create_wc(unsigned long base, unsigned long size)
{
return (struct io_mapping *) ioremap_wc(base, size);
}
static inline void
io_mapping_free(struct io_mapping *mapping)
{
iounmap(mapping);
}
/* Atomic map/unmap */
static inline void *
io_mapping_map_atomic_wc(struct io_mapping *mapping, unsigned long offset)
{
return ((char *) mapping) + offset;
}
static inline void
io_mapping_unmap_atomic(void *vaddr)
{
}
/* Non-atomic map/unmap */
static inline void *
io_mapping_map_wc(struct io_mapping *mapping, unsigned long offset)
{
return ((char *) mapping) + offset;
}
static inline void
io_mapping_unmap(void *vaddr)
{
}
#endif /* CONFIG_X86_64 */
#ifdef CONFIG_X86_32
static inline struct io_mapping *
io_mapping_create_wc(unsigned long base, unsigned long size)
{
return (struct io_mapping *) base;
}
static inline void
io_mapping_free(struct io_mapping *mapping)
{
}
/* Atomic map/unmap */
static inline void *
io_mapping_map_atomic_wc(struct io_mapping *mapping, unsigned long offset)
{
offset += (unsigned long) mapping;
return iomap_atomic_prot_pfn(offset >> PAGE_SHIFT, KM_USER0,
__pgprot(__PAGE_KERNEL_WC));
}
static inline void
io_mapping_unmap_atomic(void *vaddr)
{
iounmap_atomic(vaddr, KM_USER0);
}
static inline void *
io_mapping_map_wc(struct io_mapping *mapping, unsigned long offset)
{
offset += (unsigned long) mapping;
return ioremap_wc(offset, PAGE_SIZE);
}
static inline void
io_mapping_unmap(void *vaddr)
{
iounmap(vaddr);
}
#endif /* CONFIG_X86_32 */
#endif /* _LINUX_IO_MAPPING_H */