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
  20 static 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
  74 static 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
 109 static 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
 122 int 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 }