LXR linux/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 *   Copyright 2009 Intel Corporation; author H. Peter Anvin
   6 *
   7 *   This file is part of the Linux kernel, and is made available under
   8 *   the terms of the GNU General Public License version 2.
   9 *
  10 * ----------------------------------------------------------------------- */
  11
  12/*
  13 * Memory detection code
  14 */
  15
  16#include "boot.h"
  17
  18#define SMAP    0x534d4150      /* ASCII "SMAP" */
  19
  20static int detect_memory_e820(void)
  21{
  22        int count = 0;
  23        struct biosregs ireg, oreg;
  24        struct e820entry *desc = boot_params.e820_map;
  25        static struct e820entry buf; /* static so it is zeroed */
  26
  27        initregs(&ireg);
  28        ireg.ax  = 0xe820;
  29        ireg.cx  = sizeof buf;
  30        ireg.edx = SMAP;
  31        ireg.di  = (size_t)&buf;
  32
  33        /*
  34         * Note: at least one BIOS is known which assumes that the
  35         * buffer pointed to by one e820 call is the same one as
  36         * the previous call, and only changes modified fields.  Therefore,
  37         * we use a temporary buffer and copy the results entry by entry.
  38         *
  39         * This routine deliberately does not try to account for
  40         * ACPI 3+ extended attributes.  This is because there are
  41         * BIOSes in the field which report zero for the valid bit for
  42         * all ranges, and we don't currently make any use of the
  43         * other attribute bits.  Revisit this if we see the extended
  44         * attribute bits deployed in a meaningful way in the future.
  45         */
  46
  47        do {
  48                intcall(0x15, &ireg, &oreg);
  49                ireg.ebx = oreg.ebx; /* for next iteration... */
  50
  51                /* BIOSes which terminate the chain with CF = 1 as opposed
  52                   to %ebx = 0 don't always report the SMAP signature on
  53                   the final, failing, probe. */
  54                if (oreg.eflags & X86_EFLAGS_CF)
  55                        break;
  56
  57                /* Some BIOSes stop returning SMAP in the middle of
  58                   the search loop.  We don't know exactly how the BIOS
  59                   screwed up the map at that point, we might have a
  60                   partial map, the full map, or complete garbage, so
  61                   just return failure. */
  62                if (oreg.eax != SMAP) {
  63                        count = 0;
  64                        break;
  65                }
  66
  67                *desc++ = buf;
  68                count++;
  69        } while (ireg.ebx && count < ARRAY_SIZE(boot_params.e820_map));
  70
  71        return boot_params.e820_entries = count;
  72}
  73
  74static int detect_memory_e801(void)
  75{
  76        struct biosregs ireg, oreg;
  77
  78        initregs(&ireg);
  79        ireg.ax = 0xe801;
  80        intcall(0x15, &ireg, &oreg);
  81
  82        if (oreg.eflags & X86_EFLAGS_CF)
  83                return -1;
  84
  85        /* Do we really need to do this? */
  86        if (oreg.cx || oreg.dx) {
  87                oreg.ax = oreg.cx;
  88                oreg.bx = oreg.dx;
  89        }
  90
  91        if (oreg.ax > 15*1024) {
  92                return -1;      /* Bogus! */
  93        } else if (oreg.ax == 15*1024) {
  94                boot_params.alt_mem_k = (oreg.bx << 6) + oreg.ax;
  95        } else {
  96                /*
  97                 * This ignores memory above 16MB if we have a memory
  98                 * hole there.  If someone actually finds a machine
  99                 * with a memory hole at 16MB and no support for
 100                 * 0E820h they should probably generate a fake e820
 101                 * map.
 102                 */
 103                boot_params.alt_mem_k = oreg.ax;
 104        }
 105
 106        return 0;
 107}
 108
 109static int detect_memory_88(void)
 110{
 111        struct biosregs ireg, oreg;
 112
 113        initregs(&ireg);
 114        ireg.ah = 0x88;
 115        intcall(0x15, &ireg, &oreg);
 116
 117        boot_params.screen_info.ext_mem_k = oreg.ax;
 118
 119        return -(oreg.eflags & X86_EFLAGS_CF); /* 0 or -1 */
 120}
 121
 122int detect_memory(void)
 123{
 124        int err = -1;
 125
 126        if (detect_memory_e820() > 0)
 127                err = 0;
 128
 129        if (!detect_memory_e801())
 130                err = 0;
 131
 132        if (!detect_memory_88())
 133                err = 0;
 134
 135        return err;
 136}
 137