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/arch/x86/boot/memory.c

https://bitbucket.org/thekraven/iscream_thunderc-2.6.35
C | 136 lines | 68 code | 26 blank | 42 comment | 16 complexity | 8a6b8eb44b62a5b1898dcb462e620c72 MD5 | raw file
Possible License(s): GPL-2.0, LGPL-2.0, AGPL-1.0
  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
 20static 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
 74static 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.dx << 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
109static 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
122int 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}