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