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

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.

/*

 * 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 */