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authorMikael Pettersson <mikpe@it.uu.se>2007-07-24 00:25:59 +0200
committerH. Peter Anvin <hpa@zytor.com>2007-07-25 12:02:21 -0700
commit1514ab09edb071345fe17cd230c97f9e72c9478e (patch)
tree209b45d07415b73fdf1110f421575ab7942c2a52 /Documentation/driver-model/interface.txt
parent80492cc797ea15572de8eac766cbf606626ee338 (diff)
[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? */ 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>
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