39b68976ac
When we use BIOS function e801 to probe memory, we should use ax/bx (or cx/dx) as a pair, not mix and match. This was a typo during the translation from assembly code, and breaks at least one set of machines in the field (which return cx = dx = 0). Reported-and-tested-by: Chris Samuel <chris@csamuel.org> Fix-proposed-by: Thomas Meyer <thomas@m3y3r.de> Link: http://lkml.kernel.org/r/1303566747.12067.10.camel@localhost.localdomain
136 lines
3.3 KiB
C
136 lines
3.3 KiB
C
/* -*- linux-c -*- ------------------------------------------------------- *
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*
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* Copyright (C) 1991, 1992 Linus Torvalds
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* Copyright 2007 rPath, Inc. - All Rights Reserved
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* Copyright 2009 Intel Corporation; author H. Peter Anvin
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*
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* This file is part of the Linux kernel, and is made available under
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* the terms of the GNU General Public License version 2.
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*
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* ----------------------------------------------------------------------- */
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/*
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* Memory detection code
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*/
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#include "boot.h"
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#define SMAP 0x534d4150 /* ASCII "SMAP" */
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static int detect_memory_e820(void)
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{
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int count = 0;
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struct biosregs ireg, oreg;
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struct e820entry *desc = boot_params.e820_map;
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static struct e820entry buf; /* static so it is zeroed */
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initregs(&ireg);
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ireg.ax = 0xe820;
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ireg.cx = sizeof buf;
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ireg.edx = SMAP;
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ireg.di = (size_t)&buf;
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/*
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* Note: at least one BIOS is known which assumes that the
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* buffer pointed to by one e820 call is the same one as
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* the previous call, and only changes modified fields. Therefore,
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* we use a temporary buffer and copy the results entry by entry.
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*
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* This routine deliberately does not try to account for
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* ACPI 3+ extended attributes. This is because there are
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* BIOSes in the field which report zero for the valid bit for
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* all ranges, and we don't currently make any use of the
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* other attribute bits. Revisit this if we see the extended
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* attribute bits deployed in a meaningful way in the future.
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*/
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do {
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intcall(0x15, &ireg, &oreg);
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ireg.ebx = oreg.ebx; /* for next iteration... */
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/* BIOSes which terminate the chain with CF = 1 as opposed
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to %ebx = 0 don't always report the SMAP signature on
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the final, failing, probe. */
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if (oreg.eflags & X86_EFLAGS_CF)
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break;
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/* Some BIOSes stop returning SMAP in the middle of
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the search loop. We don't know exactly how the BIOS
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screwed up the map at that point, we might have a
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partial map, the full map, or complete garbage, so
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just return failure. */
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if (oreg.eax != SMAP) {
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count = 0;
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break;
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}
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*desc++ = buf;
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count++;
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} while (ireg.ebx && count < ARRAY_SIZE(boot_params.e820_map));
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return boot_params.e820_entries = count;
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}
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static int detect_memory_e801(void)
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{
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struct biosregs ireg, oreg;
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initregs(&ireg);
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ireg.ax = 0xe801;
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intcall(0x15, &ireg, &oreg);
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if (oreg.eflags & X86_EFLAGS_CF)
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return -1;
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/* Do we really need to do this? */
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if (oreg.cx || oreg.dx) {
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oreg.ax = oreg.cx;
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oreg.bx = oreg.dx;
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}
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if (oreg.ax > 15*1024) {
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return -1; /* Bogus! */
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} else if (oreg.ax == 15*1024) {
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boot_params.alt_mem_k = (oreg.bx << 6) + oreg.ax;
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} else {
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/*
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* This ignores memory above 16MB if we have a memory
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* hole there. If someone actually finds a machine
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* with a memory hole at 16MB and no support for
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* 0E820h they should probably generate a fake e820
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* map.
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*/
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boot_params.alt_mem_k = oreg.ax;
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}
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return 0;
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}
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static int detect_memory_88(void)
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{
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struct biosregs ireg, oreg;
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initregs(&ireg);
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ireg.ah = 0x88;
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intcall(0x15, &ireg, &oreg);
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boot_params.screen_info.ext_mem_k = oreg.ax;
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return -(oreg.eflags & X86_EFLAGS_CF); /* 0 or -1 */
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}
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int detect_memory(void)
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{
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int err = -1;
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if (detect_memory_e820() > 0)
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err = 0;
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if (!detect_memory_e801())
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err = 0;
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if (!detect_memory_88())
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err = 0;
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return err;
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}
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