arch/i386/boot/memory.c

   1 /* -*- linux-c -*- ------------------------------------------------------- *
   2  *
   3  *   Copyright (C) 1991, 1992 Linus Torvalds
   4  *   Copyright 2007 rPath, Inc. - All Rights Reserved
   5  *
   6  *   This file is part of the Linux kernel, and is made available under
   7  *   the terms of the GNU General Public License version 2.
   8  *
   9  * ----------------------------------------------------------------------- */
  10
  11 /*
  12  * arch/i386/boot/memory.c
  13  *
  14  * Memory detection code
  15  */
  16
  17 #include "boot.h"
  18
  19 #define SMAP    0x534d4150      /* ASCII "SMAP" */
  20
  21 static int detect_memory_e820(void)
  22 {
  23         u32 next = 0;
  24         u32 size, id;
  25         u8 err;
  26         struct e820entry *desc = boot_params.e820_map;
  27
  28         do {
  29                 size = sizeof(struct e820entry);
  30                 id = SMAP;
  31                 asm("int $0x15; setc %0"
  32                     : "=am" (err), "+b" (next), "+d" (id), "+c" (size),
  33                       "=m" (*desc)
  34                     : "D" (desc), "a" (0xe820));
  35
  36                 if (err || id != SMAP)
  37                         break;
  38
  39                 boot_params.e820_entries++;
  40                 desc++;
  41         } while (next && boot_params.e820_entries < E820MAX);
  42
  43         return boot_params.e820_entries;
  44 }
  45
  46 static int detect_memory_e801(void)
  47 {
  48         u16 ax, bx, cx, dx;
  49         u8 err;
  50
  51         bx = cx = dx = 0;
  52         ax = 0xe801;
  53         asm("stc; int $0x15; setc %0"
  54             : "=m" (err), "+a" (ax), "+b" (bx), "+c" (cx), "+d" (dx));
  55
  56         if (err)
  57                 return -1;
  58
  59         /* Do we really need to do this? */
  60         if (cx || dx) {
  61                 ax = cx;
  62                 bx = dx;
  63         }
  64
  65         if (ax > 15*1024)
  66                 return -1;      /* Bogus! */
  67
  68         /* This ignores memory above 16MB if we have a memory hole
  69            there.  If someone actually finds a machine with a memory
  70            hole at 16MB and no support for 0E820h they should probably
  71            generate a fake e820 map. */
  72         boot_params.alt_mem_k = (ax == 15*1024) ? (dx << 6)+ax : ax;
  73
  74         return 0;
  75 }
  76
  77 static int detect_memory_88(void)
  78 {
  79         u16 ax;
  80         u8 err;
  81
  82         ax = 0x8800;
  83         asm("stc; int $0x15; setc %0" : "=bcdm" (err), "+a" (ax));
  84
  85         boot_params.screen_info.ext_mem_k = ax;
  86
  87         return -err;
  88 }
  89
  90 int detect_memory(void)
  91 {
  92         if (detect_memory_e820() > 0)
  93                 return 0;
  94
  95         if (!detect_memory_e801())
  96                 return 0;
  97
  98         return detect_memory_88();
  99 }