include/asm-i386/fixmap.h

   1 /*
   2  * fixmap.h: compile-time virtual memory allocation
   3  *
   4  * This file is subject to the terms and conditions of the GNU General Public
   5  * License.  See the file "COPYING" in the main directory of this archive
   6  * for more details.
   7  *
   8  * Copyright (C) 1998 Ingo Molnar
   9  */
  10
  11 #ifndef _ASM_FIXMAP_H
  12 #define _ASM_FIXMAP_H
  13
  14 #include <asm/page.h>
  15 #include <linux/kernel.h>
  16
  17 /*
  18  * Here we define all the compile-time 'special' virtual
  19  * addresses. The point is to have a constant address at
  20  * compile time, but to set the physical address only
  21  * in the boot process. We allocate these special  addresses
  22  * from the end of virtual memory (0xfffff000) backwards.
  23  * Also this lets us do fail-safe vmalloc(), we
  24  * can guarantee that these special addresses and
  25  * vmalloc()-ed addresses never overlap.
  26  *
  27  * these 'compile-time allocated' memory buffers are
  28  * fixed-size 4k pages. (or larger if used with an increment
  29  * bigger than 1) use fixmap_set(idx,phys) to associate
  30  * physical memory with fixmap indices.
  31  *
  32  * TLB entries of such buffers will not be flushed across
  33  * task switches.
  34  */
  35
  36 /*
  37  * on UP currently we will have no trace of the fixmap mechanizm,
  38  * no page table allocations, etc. This might change in the
  39  * future, say framebuffers for the console driver(s) could be
  40  * fix-mapped?
  41  */
  42 enum fixed_addresses {
  43 #if __SMP__
  44         FIX_APIC_BASE,
  45         FIX_IO_APIC_BASE,
  46 #endif
  47         __end_of_fixed_addresses
  48 };
  49
  50 extern void set_fixmap (enum fixed_addresses idx, unsigned long phys);
  51
  52 /*
  53  * used by vmalloc.c.
  54  *
  55  * Leave one empty page between vmalloc'ed areas and
  56  * the start of the fixmap, and leave one page empty
  57  * at the top of mem..
  58  */
  59 #define FIXADDR_TOP     (0xffffe000UL)
  60 #define FIXADDR_SIZE    (__end_of_fixed_addresses << PAGE_SHIFT)
  61 #define FIXADDR_START   (FIXADDR_TOP - FIXADDR_SIZE)
  62
  63 #define __fix_to_virt(x)        (FIXADDR_TOP - ((x) << PAGE_SHIFT))
  64
  65 extern void __this_fixmap_does_not_exist(void);
  66
  67 /*
  68  * 'index to address' translation. If anyone tries to use the idx
  69  * directly without tranlation, we catch the bug with a NULL-deference
  70  * kernel oops. Illegal ranges of incoming indices are caught too.
  71  */
  72 extern inline unsigned long fix_to_virt(const unsigned int idx)
  73 {
  74         /*
  75          * this branch gets completely eliminated after inlining,
  76          * except when someone tries to use fixaddr indices in an
  77          * illegal way. (such as mixing up address types or using
  78          * out-of-range indices).
  79          *
  80          * If it doesn't get removed, the linker will complain
  81          * loudly with a reasonably clear error message..
  82          */
  83         if (idx >= __end_of_fixed_addresses)
  84                 __this_fixmap_does_not_exist();
  85
  86         return __fix_to_virt(idx);
  87 }
  88
  89 #endif