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 * arch/i386/boot/memory.c 13 * 14 * Memory detection code 15 */ 16 17 #include "boot.h" 18 19 #define SMAP 0x534d4150 /* ASCII "SMAP" */ 20 21 static int detect_memory_e820(void) 22 { 23 int count = 0; 24 u32 next = 0; 25 u32 size, id; 26 u8 err; 27 struct e820entry *desc = boot_params.e820_map; 28 29 do { 30 size = sizeof(struct e820entry); 31 32 /* Important: %edx is clobbered by some BIOSes, 33 so it must be either used for the error output 34 or explicitly marked clobbered. */ 35 asm("int $0x15; setc %0" 36 : "=d" (err), "+b" (next), "=a" (id), "+c" (size), 37 "=m" (*desc) 38 : "D" (desc), "d" (SMAP), "a" (0xe820)); 39 40 /* Some BIOSes stop returning SMAP in the middle of 41 the search loop. We don't know exactly how the BIOS 42 screwed up the map at that point, we might have a 43 partial map, the full map, or complete garbage, so 44 just return failure. */ 45 if (id != SMAP) { 46 count = 0; 47 break; 48 } 49 50 if (err) 51 break; 52 53 count++; 54 desc++; 55 } while (next && count < E820MAX); 56 57 return boot_params.e820_entries = count; 58 } 59 60 static int detect_memory_e801(void) 61 { 62 u16 ax, bx, cx, dx; 63 u8 err; 64 65 bx = cx = dx = 0; 66 ax = 0xe801; 67 asm("stc; int $0x15; setc %0" 68 : "=m" (err), "+a" (ax), "+b" (bx), "+c" (cx), "+d" (dx)); 69 70 if (err) 71 return -1; 72 73 /* Do we really need to do this? */ 74 if (cx || dx) { 75 ax = cx; 76 bx = dx; 77 } 78 79 if (ax > 15*1024) 80 return -1; /* Bogus! */ 81 82 /* This ignores memory above 16MB if we have a memory hole 83 there. If someone actually finds a machine with a memory 84 hole at 16MB and no support for 0E820h they should probably 85 generate a fake e820 map. */ 86 boot_params.alt_mem_k = (ax == 15*1024) ? (dx << 6)+ax : ax; 87 88 return 0; 89 } 90 91 static int detect_memory_88(void) 92 { 93 u16 ax; 94 u8 err; 95 96 ax = 0x8800; 97 asm("stc; int $0x15; setc %0" : "=bcdm" (err), "+a" (ax)); 98 99 boot_params.screen_info.ext_mem_k = ax; 100 101 return -err; 102 } 103 104 int detect_memory(void) 105 { 106 int err = -1; 107 108 if (detect_memory_e820() > 0) 109 err = 0; 110 111 if (!detect_memory_e801()) 112 err = 0; 113 114 if (!detect_memory_88()) 115 err = 0; 116 117 return err; 118 } 119