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fixmap.h

/*
 * fixmap.h: compile-time virtual memory allocation
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (C) 1998 Ingo Molnar
 *
 * Support of BIGMEM added by Gerhard Wichert, Siemens AG, July 1999
 */

#ifndef _ASM_FIXMAP_H
#define _ASM_FIXMAP_H

#include <linux/kernel.h>
#include <asm/page.h>
#ifdef CONFIG_HIGHMEM
#include <linux/threads.h>
#include <asm/kmap_types.h>
#endif

/*
 * Here we define all the compile-time 'special' virtual
 * addresses. The point is to have a constant address at
 * compile time, but to set the physical address only
 * in the boot process. We allocate these special  addresses
 * from the end of P3 backwards.
 * Also this lets us do fail-safe vmalloc(), we
 * can guarantee that these special addresses and
 * vmalloc()-ed addresses never overlap.
 *
 * these 'compile-time allocated' memory buffers are
 * fixed-size 4k pages. (or larger if used with an increment
 * highger than 1) use fixmap_set(idx,phys) to associate
 * physical memory with fixmap indices.
 *
 * TLB entries of such buffers will not be flushed across
 * task switches.
 */

/*
 * on UP currently we will have no trace of the fixmap mechanizm,
 * no page table allocations, etc. This might change in the
 * future, say framebuffers for the console driver(s) could be
 * fix-mapped?
 */
enum fixed_addresses {
#define FIX_N_COLOURS 16
      FIX_CMAP_BEGIN,
      FIX_CMAP_END = FIX_CMAP_BEGIN + FIX_N_COLOURS,
      FIX_UNCACHED,
#ifdef CONFIG_HIGHMEM
      FIX_KMAP_BEGIN,   /* reserved pte's for temporary kernel mappings */
      FIX_KMAP_END = FIX_KMAP_BEGIN+(KM_TYPE_NR*NR_CPUS)-1,
#endif
      __end_of_fixed_addresses
};

extern void __set_fixmap(enum fixed_addresses idx,
                   unsigned long phys, pgprot_t flags);

#define set_fixmap(idx, phys) \
            __set_fixmap(idx, phys, PAGE_KERNEL)
/*
 * Some hardware wants to get fixmapped without caching.
 */
#define set_fixmap_nocache(idx, phys) \
            __set_fixmap(idx, phys, PAGE_KERNEL_NOCACHE)
/*
 * used by vmalloc.c.
 *
 * Leave one empty page between vmalloc'ed areas and
 * the start of the fixmap, and leave one page empty
 * at the top of mem..
 */
#ifdef CONFIG_SUPERH32
#define FIXADDR_TOP     (P4SEG - PAGE_SIZE)
#else
#define FIXADDR_TOP     (0xff000000 - PAGE_SIZE)
#endif
#define FIXADDR_SIZE    (__end_of_fixed_addresses << PAGE_SHIFT)
#define FIXADDR_START   (FIXADDR_TOP - FIXADDR_SIZE)

#define __fix_to_virt(x)      (FIXADDR_TOP - ((x) << PAGE_SHIFT))
#define __virt_to_fix(x)      ((FIXADDR_TOP - ((x)&PAGE_MASK)) >> PAGE_SHIFT)

extern void __this_fixmap_does_not_exist(void);

/*
 * 'index to address' translation. If anyone tries to use the idx
 * directly without tranlation, we catch the bug with a NULL-deference
 * kernel oops. Illegal ranges of incoming indices are caught too.
 */
static inline unsigned long fix_to_virt(const unsigned int idx)
{
      /*
       * this branch gets completely eliminated after inlining,
       * except when someone tries to use fixaddr indices in an
       * illegal way. (such as mixing up address types or using
       * out-of-range indices).
       *
       * If it doesn't get removed, the linker will complain
       * loudly with a reasonably clear error message..
       */
      if (idx >= __end_of_fixed_addresses)
            __this_fixmap_does_not_exist();

        return __fix_to_virt(idx);
}

static inline unsigned long virt_to_fix(const unsigned long vaddr)
{
      BUG_ON(vaddr >= FIXADDR_TOP || vaddr < FIXADDR_START);
      return __virt_to_fix(vaddr);
}
#endif

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