1 // SPDX-License-Identifier: GPL-2.0-only 2 /* -*- linux-c -*- ------------------------------------------------------- * 3 * 4 * Copyright (C) 1991, 1992 Linus Torvalds 5 * Copyright 2007 rPath, Inc. - All Rights Reserved 6 * Copyright 2009 Intel Corporation; author H. Peter Anvin 7 * 8 * ----------------------------------------------------------------------- */ 9 10 /* 11 * Memory detection code 12 */ 13 14 #include "boot.h" 15 16 #define SMAP 0x534d4150 /* ASCII "SMAP" */ 17 18 static void detect_memory_e820(void) 19 { 20 int count = 0; 21 struct biosregs ireg, oreg; 22 struct boot_e820_entry *desc = boot_params.e820_table; 23 static struct boot_e820_entry buf; /* static so it is zeroed */ 24 25 initregs(&ireg); 26 ireg.ax = 0xe820; 27 ireg.cx = sizeof(buf); 28 ireg.edx = SMAP; 29 ireg.di = (size_t)&buf; 30 31 /* 32 * Note: at least one BIOS is known which assumes that the 33 * buffer pointed to by one e820 call is the same one as 34 * the previous call, and only changes modified fields. Therefore, 35 * we use a temporary buffer and copy the results entry by entry. 36 * 37 * This routine deliberately does not try to account for 38 * ACPI 3+ extended attributes. This is because there are 39 * BIOSes in the field which report zero for the valid bit for 40 * all ranges, and we don't currently make any use of the 41 * other attribute bits. Revisit this if we see the extended 42 * attribute bits deployed in a meaningful way in the future. 43 */ 44 45 do { 46 intcall(0x15, &ireg, &oreg); 47 ireg.ebx = oreg.ebx; /* for next iteration... */ 48 49 /* BIOSes which terminate the chain with CF = 1 as opposed 50 to %ebx = 0 don't always report the SMAP signature on 51 the final, failing, probe. */ 52 if (oreg.eflags & X86_EFLAGS_CF) 53 break; 54 55 /* Some BIOSes stop returning SMAP in the middle of 56 the search loop. We don't know exactly how the BIOS 57 screwed up the map at that point, we might have a 58 partial map, the full map, or complete garbage, so 59 just return failure. */ 60 if (oreg.eax != SMAP) { 61 count = 0; 62 break; 63 } 64 65 *desc++ = buf; 66 count++; 67 } while (ireg.ebx && count < ARRAY_SIZE(boot_params.e820_table)); 68 69 boot_params.e820_entries = count; 70 } 71 72 static void detect_memory_e801(void) 73 { 74 struct biosregs ireg, oreg; 75 76 initregs(&ireg); 77 ireg.ax = 0xe801; 78 intcall(0x15, &ireg, &oreg); 79 80 if (oreg.eflags & X86_EFLAGS_CF) 81 return; 82 83 /* Do we really need to do this? */ 84 if (oreg.cx || oreg.dx) { 85 oreg.ax = oreg.cx; 86 oreg.bx = oreg.dx; 87 } 88 89 if (oreg.ax > 15*1024) { 90 return; /* Bogus! */ 91 } else if (oreg.ax == 15*1024) { 92 boot_params.alt_mem_k = (oreg.bx << 6) + oreg.ax; 93 } else { 94 /* 95 * This ignores memory above 16MB if we have a memory 96 * hole there. If someone actually finds a machine 97 * with a memory hole at 16MB and no support for 98 * 0E820h they should probably generate a fake e820 99 * map. 100 */ 101 boot_params.alt_mem_k = oreg.ax; 102 } 103 } 104 105 static void detect_memory_88(void) 106 { 107 struct biosregs ireg, oreg; 108 109 initregs(&ireg); 110 ireg.ah = 0x88; 111 intcall(0x15, &ireg, &oreg); 112 113 boot_params.screen_info.ext_mem_k = oreg.ax; 114 } 115 116 void detect_memory(void) 117 { 118 detect_memory_e820(); 119 120 detect_memory_e801(); 121 122 detect_memory_88(); 123 } 124