• Mikael Pettersson's avatar
    [x86 setup] APM detection logic bug fix · 1514ab09
    Mikael Pettersson authored
    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: default avatarMikael Pettersson <mikpe@it.uu.se>
    Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
    1514ab09
apm.c 2.41 KB