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         u32 next = 0;
  24         u32 size, id, edi;
  25         u8 err;
  26         struct e820entry *desc = boot_params.e820_map;
  27         static struct e820entry buf; /* static so it is zeroed */
  28
  29         /*
  30          * Note: at least one BIOS is known which assumes that the
  31          * buffer pointed to by one e820 call is the same one as
  32          * the previous call, and only changes modified fields.  Therefore,
  33          * we use a temporary buffer and copy the results entry by entry.
  34          *
  35          * This routine deliberately does not try to account for
  36          * ACPI 3+ extended attributes.  This is because there are
  37          * BIOSes in the field which report zero for the valid bit for
  38          * all ranges, and we don't currently make any use of the
  39          * other attribute bits.  Revisit this if we see the extended
  40          * attribute bits deployed in a meaningful way in the future.
  41          */
  42
  43         do {
  44                 size = sizeof buf;
  45
  46                 /* Important: %edx and %esi are clobbered by some BIOSes,
  47                    so they must be either used for the error output
  48                    or explicitly marked clobbered.  Given that, assume there
  49                    is something out there clobbering %ebp and %edi, too. */
  50                 asm("pushl %%ebp; int $0x15; popl %%ebp; setc %0"
  51                     : "=d" (err), "+b" (next), "=a" (id), "+c" (size),
  52                       "=D" (edi), "+m" (buf)
  53                     : "D" (&buf), "d" (SMAP), "a" (0xe820)
  54                     : "esi");
  55
  56                 /* BIOSes which terminate the chain with CF = 1 as opposed
  57                    to %ebx = 0 don't always report the SMAP signature on
  58                    the final, failing, probe. */
  59                 if (err)
  60                         break;
  61
  62                 /* Some BIOSes stop returning SMAP in the middle of
  63                    the search loop.  We don't know exactly how the BIOS
  64                    screwed up the map at that point, we might have a
  65                    partial map, the full map, or complete garbage, so
  66                    just return failure. */
  67                 if (id != SMAP) {
  68                         count = 0;
  69                         break;
  70                 }
  71
  72                 *desc++ = buf;
  73                 count++;
  74         } while (next && count < ARRAY_SIZE(boot_params.e820_map));
  75
  76         return boot_params.e820_entries = count;
  77 }
  78
  79 static int detect_memory_e801(void)
  80 {
  81         u16 ax, bx, cx, dx;
  82         u8 err;
  83
  84         bx = cx = dx = 0;
  85         ax = 0xe801;
  86         asm("stc; int $0x15; setc %0"
  87             : "=m" (err), "+a" (ax), "+b" (bx), "+c" (cx), "+d" (dx));
  88
  89         if (err)
  90                 return -1;
  91
  92         /* Do we really need to do this? */
  93         if (cx || dx) {
  94                 ax = cx;
  95                 bx = dx;
  96         }
  97
  98         if (ax > 15*1024)
  99                 return -1;      /* Bogus! */
 100
 101         /* This ignores memory above 16MB if we have a memory hole
 102            there.  If someone actually finds a machine with a memory
 103            hole at 16MB and no support for 0E820h they should probably
 104            generate a fake e820 map. */
 105         boot_params.alt_mem_k = (ax == 15*1024) ? (dx << 6)+ax : ax;
 106
 107         return 0;
 108 }
 109
 110 static int detect_memory_88(void)
 111 {
 112         u16 ax;
 113         u8 err;
 114
 115         ax = 0x8800;
 116         asm("stc; int $0x15; setc %0" : "=bcdm" (err), "+a" (ax));
 117
 118         boot_params.screen_info.ext_mem_k = ax;
 119
 120         return -err;
 121 }
 122
 123 int detect_memory(void)
 124 {
 125         int err = -1;
 126
 127         if (detect_memory_e820() > 0)
 128                 err = 0;
 129
 130         if (!detect_memory_e801())
 131                 err = 0;
 132
 133         if (!detect_memory_88())
 134                 err = 0;
 135
 136         return err;
 137 }