linux/arch/x86/boot/memory.c
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   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 * Memory detection code
  13 */
  14
  15#include "boot.h"
  16
  17#define SMAP    0x534d4150      /* ASCII "SMAP" */
  18
  19static int detect_memory_e820(void)
  20{
  21        int count = 0;
  22        u32 next = 0;
  23        u32 size, id;
  24        u8 err;
  25        struct e820entry *desc = boot_params.e820_map;
  26
  27        do {
  28                size = sizeof(struct e820entry);
  29
  30                /* Important: %edx and %esi are clobbered by some BIOSes,
  31                   so they must be either used for the error output
  32                   or explicitly marked clobbered. */
  33                asm("int $0x15; setc %0"
  34                    : "=d" (err), "+b" (next), "=a" (id), "+c" (size),
  35                      "=m" (*desc)
  36                    : "D" (desc), "d" (SMAP), "a" (0xe820)
  37                    : "esi");
  38
  39                /* BIOSes which terminate the chain with CF = 1 as opposed
  40                   to %ebx = 0 don't always report the SMAP signature on
  41                   the final, failing, probe. */
  42                if (err)
  43                        break;
  44
  45                /* Some BIOSes stop returning SMAP in the middle of
  46                   the search loop.  We don't know exactly how the BIOS
  47                   screwed up the map at that point, we might have a
  48                   partial map, the full map, or complete garbage, so
  49                   just return failure. */
  50                if (id != SMAP) {
  51                        count = 0;
  52                        break;
  53                }
  54
  55                count++;
  56                desc++;
  57        } while (next && count < ARRAY_SIZE(boot_params.e820_map));
  58
  59        return boot_params.e820_entries = count;
  60}
  61
  62static int detect_memory_e801(void)
  63{
  64        u16 ax, bx, cx, dx;
  65        u8 err;
  66
  67        bx = cx = dx = 0;
  68        ax = 0xe801;
  69        asm("stc; int $0x15; setc %0"
  70            : "=m" (err), "+a" (ax), "+b" (bx), "+c" (cx), "+d" (dx));
  71
  72        if (err)
  73                return -1;
  74
  75        /* Do we really need to do this? */
  76        if (cx || dx) {
  77                ax = cx;
  78                bx = dx;
  79        }
  80
  81        if (ax > 15*1024)
  82                return -1;      /* Bogus! */
  83
  84        /* This ignores memory above 16MB if we have a memory hole
  85           there.  If someone actually finds a machine with a memory
  86           hole at 16MB and no support for 0E820h they should probably
  87           generate a fake e820 map. */
  88        boot_params.alt_mem_k = (ax == 15*1024) ? (dx << 6)+ax : ax;
  89
  90        return 0;
  91}
  92
  93static int detect_memory_88(void)
  94{
  95        u16 ax;
  96        u8 err;
  97
  98        ax = 0x8800;
  99        asm("stc; int $0x15; setc %0" : "=bcdm" (err), "+a" (ax));
 100
 101        boot_params.screen_info.ext_mem_k = ax;
 102
 103        return -err;
 104}
 105
 106int detect_memory(void)
 107{
 108        int err = -1;
 109
 110        if (detect_memory_e820() > 0)
 111                err = 0;
 112
 113        if (!detect_memory_e801())
 114                err = 0;
 115
 116        if (!detect_memory_88())
 117                err = 0;
 118
 119        return err;
 120}
 121