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>
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Keith Packard
Ingo Molnar
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The io_mapping functions in linux/io-mapping.h provide an abstraction for
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efficiently mapping small regions of an I/O device to the CPU. The initial
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usage is to support the large graphics aperture on 32-bit processors where
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ioremap_wc cannot be used to statically map the entire aperture to the CPU
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as it would consume too much of the kernel address space.
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A mapping object is created during driver initialization using
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struct io_mapping *io_mapping_create_wc(unsigned long base,
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unsigned long size)
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'base' is the bus address of the region to be made
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mappable, while 'size' indicates how large a mapping region to
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enable. Both are in bytes.
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This _wc variant provides a mapping which may only be used
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with the io_mapping_map_atomic_wc or io_mapping_map_wc.
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With this mapping object, individual pages can be mapped either atomically
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or not, depending on the necessary scheduling environment. Of course, atomic
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maps are more efficient:
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void *io_mapping_map_atomic_wc(struct io_mapping *mapping,
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unsigned long offset)
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'offset' is the offset within the defined mapping region.
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Accessing addresses beyond the region specified in the
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creation function yields undefined results. Using an offset
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which is not page aligned yields an undefined result. The
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return value points to a single page in CPU address space.
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This _wc variant returns a write-combining map to the
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page and may only be used with mappings created by
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io_mapping_create_wc
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Note that the task may not sleep while holding this page
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mapped.
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void io_mapping_unmap_atomic(void *vaddr)
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'vaddr' must be the the value returned by the last
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io_mapping_map_atomic_wc call. This unmaps the specified
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page and allows the task to sleep once again.
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If you need to sleep while holding the lock, you can use the non-atomic
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variant, although they may be significantly slower.
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void *io_mapping_map_wc(struct io_mapping *mapping,
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unsigned long offset)
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This works like io_mapping_map_atomic_wc except it allows
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the task to sleep while holding the page mapped.
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void io_mapping_unmap(void *vaddr)
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This works like io_mapping_unmap_atomic, except it is used
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for pages mapped with io_mapping_map_wc.
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At driver close time, the io_mapping object must be freed:
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void io_mapping_free(struct io_mapping *mapping)
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Current Implementation:
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The initial implementation of these functions uses existing mapping
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mechanisms and so provides only an abstraction layer and no new
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functionality.
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On 64-bit processors, io_mapping_create_wc calls ioremap_wc for the whole
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range, creating a permanent kernel-visible mapping to the resource. The
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map_atomic and map functions add the requested offset to the base of the
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virtual address returned by ioremap_wc.
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On 32-bit processors, io_mapping_map_atomic_wc uses io_map_atomic_prot_pfn,
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which uses the fixmaps to get us a mapping to a page using an atomic fashion.
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For io_mapping_map_wc, ioremap_wc() is used to get a mapping of the region.
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/*
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* Copyright © 2008 Keith Packard <keithp@keithp.com>
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*
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* This file is free software; you can redistribute it and/or modify
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* it under the terms of version 2 of the GNU General Public License
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* as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#ifndef _LINUX_IO_MAPPING_H
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#define _LINUX_IO_MAPPING_H
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#include <linux/types.h>
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#include <asm/io.h>
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#include <asm/page.h>
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#include <asm/iomap.h>
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/*
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* The io_mapping mechanism provides an abstraction for mapping
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* individual pages from an io device to the CPU in an efficient fashion.
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*
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* See Documentation/io_mapping.txt
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*/
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/* this struct isn't actually defined anywhere */
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struct io_mapping;
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#ifdef CONFIG_X86_64
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/* Create the io_mapping object*/
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static inline struct io_mapping *
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io_mapping_create_wc(unsigned long base, unsigned long size)
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{
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return (struct io_mapping *) ioremap_wc(base, size);
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}
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static inline void
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io_mapping_free(struct io_mapping *mapping)
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{
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iounmap(mapping);
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}
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/* Atomic map/unmap */
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static inline void *
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io_mapping_map_atomic_wc(struct io_mapping *mapping, unsigned long offset)
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{
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return ((char *) mapping) + offset;
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}
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static inline void
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io_mapping_unmap_atomic(void *vaddr)
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{
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}
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/* Non-atomic map/unmap */
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static inline void *
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io_mapping_map_wc(struct io_mapping *mapping, unsigned long offset)
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{
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return ((char *) mapping) + offset;
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}
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static inline void
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io_mapping_unmap(void *vaddr)
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{
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}
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#endif /* CONFIG_X86_64 */
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#ifdef CONFIG_X86_32
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static inline struct io_mapping *
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io_mapping_create_wc(unsigned long base, unsigned long size)
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{
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return (struct io_mapping *) base;
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}
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static inline void
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io_mapping_free(struct io_mapping *mapping)
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{
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}
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/* Atomic map/unmap */
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static inline void *
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io_mapping_map_atomic_wc(struct io_mapping *mapping, unsigned long offset)
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{
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offset += (unsigned long) mapping;
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return iomap_atomic_prot_pfn(offset >> PAGE_SHIFT, KM_USER0,
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__pgprot(__PAGE_KERNEL_WC));
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}
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static inline void
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io_mapping_unmap_atomic(void *vaddr)
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{
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iounmap_atomic(vaddr, KM_USER0);
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}
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static inline void *
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io_mapping_map_wc(struct io_mapping *mapping, unsigned long offset)
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{
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offset += (unsigned long) mapping;
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return ioremap_wc(offset, PAGE_SIZE);
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}
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static inline void
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io_mapping_unmap(void *vaddr)
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{
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iounmap(vaddr);
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}
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#endif /* CONFIG_X86_32 */
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#endif /* _LINUX_IO_MAPPING_H */
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