Author: Mikael Pettersson <[EMAIL PROTECTED]>
AuthorDate: Tue Jul 24 00:25:59 2007 +0200
Committer: H. Peter Anvin <[EMAIL PROTECTED]>
CommitDate: Wed Jul 25 12:02:21 2007 -0700
[x86 setup] APM detection logic bug fix
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? */
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 <[EMAIL PROTECTED]>
Signed-off-by: H. Peter Anvin <[EMAIL PROTECTED]>
arch/i386/boot/apm.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/arch/i386/boot/apm.c b/arch/i386/boot/apm.c
index a34087c..8be3f56 100644
@@ -40,7 +40,7 @@ int query_apm_bios(void)
if (bx != 0x504d) /* "PM" signature */
- if (cx & 0x02) /* 32 bits supported? */
+ if (!(cx & 0x02)) /* 32 bits supported? */
/* Disconnect first, just in case */
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