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[x86 setup] APM detection logic bug fix

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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>
This commit is contained in:
Mikael Pettersson 2007-07-24 00:25:59 +02:00 committed by H. Peter Anvin
parent 80492cc797
commit 1514ab09ed
1 changed files with 1 additions and 1 deletions
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2
arch/i386/boot/apm.c
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@ -40,7 +40,7 @@ int query_apm_bios(void)
if (bx != 0x504d) /* "PM" signature */
return -1;
if (cx & 0x02) /* 32 bits supported? */
if (!(cx & 0x02)) /* 32 bits supported? */
return -1;
/* Disconnect first, just in case */