arch/x86/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         int count = 0;
  24         u32 next = 0;
  25         u32 size, id;
  26         u8 err;
  27         struct e820entry *desc = boot_params.e820_map;
  28
  29         do {
  30                 size = sizeof(struct e820entry);
  31
  32                 /* Important: %edx is clobbered by some BIOSes,
  33                    so it must be either used for the error output
  34                    or explicitly marked clobbered. */
  35                 asm("int $0x15; setc %0"
  36                     : "=d" (err), "+b" (next), "=a" (id), "+c" (size),
  37                       "=m" (*desc)
  38                     : "D" (desc), "d" (SMAP), "a" (0xe820));
  39
  40                 /* Some BIOSes stop returning SMAP in the middle of
  41                    the search loop.  We don't know exactly how the BIOS
  42                    screwed up the map at that point, we might have a
  43                    partial map, the full map, or complete garbage, so
  44                    just return failure. */
  45                 if (id != SMAP) {
  46                         count = 0;
  47                         break;
  48                 }
  49
  50                 if (err)
  51                         break;
  52
  53                 count++;
  54                 desc++;
  55         } while (next && count < E820MAX);
  56
  57         return boot_params.e820_entries = count;
  58 }
  59
  60 static int detect_memory_e801(void)
  61 {
  62         u16 ax, bx, cx, dx;
  63         u8 err;
  64
  65         bx = cx = dx = 0;
  66         ax = 0xe801;
  67         asm("stc; int $0x15; setc %0"
  68             : "=m" (err), "+a" (ax), "+b" (bx), "+c" (cx), "+d" (dx));
  69
  70         if (err)
  71                 return -1;
  72
  73         /* Do we really need to do this? */
  74         if (cx || dx) {
  75                 ax = cx;
  76                 bx = dx;
  77         }
  78
  79         if (ax > 15*1024)
  80                 return -1;      /* Bogus! */
  81
  82         /* This ignores memory above 16MB if we have a memory hole
  83            there.  If someone actually finds a machine with a memory
  84            hole at 16MB and no support for 0E820h they should probably
  85            generate a fake e820 map. */
  86         boot_params.alt_mem_k = (ax == 15*1024) ? (dx << 6)+ax : ax;
  87
  88         return 0;
  89 }
  90
  91 static int detect_memory_88(void)
  92 {
  93         u16 ax;
  94         u8 err;
  95
  96         ax = 0x8800;
  97         asm("stc; int $0x15; setc %0" : "=bcdm" (err), "+a" (ax));
  98
  99         boot_params.screen_info.ext_mem_k = ax;
 100
 101         return -err;
 102 }
 103
 104 int detect_memory(void)
 105 {
 106         int err = -1;
 107
 108         if (detect_memory_e820() > 0)
 109                 err = 0;
 110
 111         if (!detect_memory_e801())
 112                 err = 0;
 113
 114         if (!detect_memory_88())
 115                 err = 0;
 116
 117         return err;
 118 }