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 struct e820_ext_entry {
  21         struct e820entry std;
  22         u32 ext_flags;
  23 } __attribute__((packed));
  24
  25 static int detect_memory_e820(void)
  26 {
  27         int count = 0;
  28         u32 next = 0;
  29         u32 size, id, edi;
  30         u8 err;
  31         struct e820entry *desc = boot_params.e820_map;
  32         static struct e820_ext_entry buf; /* static so it is zeroed */
  33
  34         /*
  35          * Set this here so that if the BIOS doesn't change this field
  36          * but still doesn't change %ecx, we're still okay...
  37          */
  38         buf.ext_flags = 1;
  39
  40         do {
  41                 size = sizeof buf;
  42
  43                 /* Important: %edx and %esi are clobbered by some BIOSes,
  44                    so they must be either used for the error output
  45                    or explicitly marked clobbered.  Given that, assume there
  46                    is something out there clobbering %ebp and %edi, too. */
  47                 asm("pushl %%ebp; int $0x15; popl %%ebp; setc %0"
  48                     : "=d" (err), "+b" (next), "=a" (id), "+c" (size),
  49                       "=D" (edi), "+m" (buf)
  50                     : "D" (&buf), "d" (SMAP), "a" (0xe820)
  51                     : "esi");
  52
  53                 /* BIOSes which terminate the chain with CF = 1 as opposed
  54                    to %ebx = 0 don't always report the SMAP signature on
  55                    the final, failing, probe. */
  56                 if (err)
  57                         break;
  58
  59                 /* Some BIOSes stop returning SMAP in the middle of
  60                    the search loop.  We don't know exactly how the BIOS
  61                    screwed up the map at that point, we might have a
  62                    partial map, the full map, or complete garbage, so
  63                    just return failure. */
  64                 if (id != SMAP) {
  65                         count = 0;
  66                         break;
  67                 }
  68
  69                 /* ACPI 3.0 added the extended flags support.  If bit 0
  70                    in the extended flags is zero, we're supposed to simply
  71                    ignore the entry -- a backwards incompatible change! */
  72                 if (size > 20 && !(buf.ext_flags & 1))
  73                         continue;
  74
  75                 *desc++ = buf.std;
  76                 count++;
  77         } while (next && count < ARRAY_SIZE(boot_params.e820_map));
  78
  79         return boot_params.e820_entries = count;
  80 }
  81
  82 static int detect_memory_e801(void)
  83 {
  84         u16 ax, bx, cx, dx;
  85         u8 err;
  86
  87         bx = cx = dx = 0;
  88         ax = 0xe801;
  89         asm("stc; int $0x15; setc %0"
  90             : "=m" (err), "+a" (ax), "+b" (bx), "+c" (cx), "+d" (dx));
  91
  92         if (err)
  93                 return -1;
  94
  95         /* Do we really need to do this? */
  96         if (cx || dx) {
  97                 ax = cx;
  98                 bx = dx;
  99         }
 100
 101         if (ax > 15*1024)
 102                 return -1;      /* Bogus! */
 103
 104         /* This ignores memory above 16MB if we have a memory hole
 105            there.  If someone actually finds a machine with a memory
 106            hole at 16MB and no support for 0E820h they should probably
 107            generate a fake e820 map. */
 108         boot_params.alt_mem_k = (ax == 15*1024) ? (dx << 6)+ax : ax;
 109
 110         return 0;
 111 }
 112
 113 static int detect_memory_88(void)
 114 {
 115         u16 ax;
 116         u8 err;
 117
 118         ax = 0x8800;
 119         asm("stc; int $0x15; setc %0" : "=bcdm" (err), "+a" (ax));
 120
 121         boot_params.screen_info.ext_mem_k = ax;
 122
 123         return -err;
 124 }
 125
 126 int detect_memory(void)
 127 {
 128         int err = -1;
 129
 130         if (detect_memory_e820() > 0)
 131                 err = 0;
 132
 133         if (!detect_memory_e801())
 134                 err = 0;
 135
 136         if (!detect_memory_88())
 137                 err = 0;
 138
 139         return err;
 140 }