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Starting with kernel 2.6.23-rc1, the i386 APM driver fails on several of my machines with the message: apm: BIOS not found This happens because of a bug in the i386 boot code rewrite from assembler to C. The original assembly code had the following code in its APM BIOS presence test (boot/setup.S): andw $0x02, %cx # Is 32 bit supported? je done_apm_bios # No 32-bit, no (good) APM BIOS That is, the code bails out if bit 2 is zero. In the new C version, this is coded as (boot/apm.c): if (cx & 0x02) /* 32 bits supported? */ return -1; Here we see that the test has been accidentally inverted. The fix is to negate the test. I've verified that this allows the APM driver to work again on my affected machines. Signed-off-by: Mikael Pettersson <mikpe@it.uu.se> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
98 lines
2.4 KiB
C
98 lines
2.4 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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*
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* Original APM BIOS checking by Stephen Rothwell, May 1994
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* (sfr@canb.auug.org.au)
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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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* arch/i386/boot/apm.c
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*
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* Get APM BIOS information
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*/
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#include "boot.h"
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#if defined(CONFIG_APM) || defined(CONFIG_APM_MODULE)
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int query_apm_bios(void)
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{
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u16 ax, bx, cx, dx, di;
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u32 ebx, esi;
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u8 err;
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/* APM BIOS installation check */
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ax = 0x5300;
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bx = cx = 0;
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asm volatile("pushl %%ebp ; int $0x15 ; popl %%ebp ; setc %0"
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: "=d" (err), "+a" (ax), "+b" (bx), "+c" (cx)
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: : "esi", "edi");
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if (err)
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return -1; /* No APM BIOS */
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if (bx != 0x504d) /* "PM" signature */
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return -1;
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if (!(cx & 0x02)) /* 32 bits supported? */
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return -1;
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/* Disconnect first, just in case */
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ax = 0x5304;
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asm volatile("pushl %%ebp ; int $0x15 ; popl %%ebp"
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: "+a" (ax)
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: : "ebx", "ecx", "edx", "esi", "edi");
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/* Paranoia */
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ebx = esi = 0;
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cx = dx = di = 0;
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/* 32-bit connect */
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asm volatile("pushl %%ebp ; int $0x15 ; popl %%ebp ; setc %6"
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: "=a" (ax), "+b" (ebx), "+c" (cx), "+d" (dx),
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"+S" (esi), "+D" (di), "=m" (err)
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: "a" (0x5303));
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boot_params.apm_bios_info.cseg = ax;
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boot_params.apm_bios_info.offset = ebx;
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boot_params.apm_bios_info.cseg_16 = cx;
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boot_params.apm_bios_info.dseg = dx;
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boot_params.apm_bios_info.cseg_len = (u16)esi;
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boot_params.apm_bios_info.cseg_16_len = esi >> 16;
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boot_params.apm_bios_info.dseg_len = di;
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if (err)
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return -1;
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/* Redo the installation check as the 32-bit connect;
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some BIOSes return different flags this way... */
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ax = 0x5300;
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bx = cx = 0;
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asm volatile("pushl %%ebp ; int $0x15 ; popl %%ebp ; setc %0"
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: "=d" (err), "+a" (ax), "+b" (bx), "+c" (cx)
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: : "esi", "edi");
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if (err || bx != 0x504d) {
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/* Failure with 32-bit connect, try to disconect and ignore */
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ax = 0x5304;
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bx = 0;
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asm volatile("pushl %%ebp ; int $0x15 ; popl %%ebp"
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: "+a" (ax), "+b" (bx)
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: : "ecx", "edx", "esi", "edi");
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return -1;
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}
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boot_params.apm_bios_info.version = ax;
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boot_params.apm_bios_info.flags = cx;
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return 0;
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}
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#endif
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