Messages in this thread Patch in this message |  | | Date | Tue, 05 Dec 2000 15:30:44 -0800 | From | "H. Peter Anvin" <> | Subject | That horrible hack from hell called A20 |
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Okay, here is my latest attempt to find a way to toggle A20M# that genuinely works on all machines -- including Olivettis, IBM Aptivas, bizarre notebooks, yadda yadda.
The bizarre notebooks with broken SMM code are the ones I really worry most about... there may very well be NO WAY to support them that actually works on all machines, because you don't get any kind of feedback that they are broken.
If you have had A20M# problems with any kernel -- recent or not -- *please* try this patch, against 2.4.0-test12-pre5:
ftp://ftp.kernel.org/pub/linux/kernel/people/hpa/a20-test12-pre5.diff
--- arch/i386/boot/setup.S.12p5 Tue Dec 5 15:19:10 2000 +++ arch/i386/boot/setup.S Tue Dec 5 15:22:13 2000 @@ -636,6 +636,7 @@ # First, try the "fast A20 gate". # inb $0x92,%al + movb %al,%dl orb $0x02,%al # Fast A20 on andb $0xfe,%al # Don't reset CPU! outb %al,$0x92 @@ -648,9 +649,17 @@ # did the trick and stop its probing at that stage; but subsequent ones # must not do so. # + pushw %dx movb $0x01,%dl # A20-sensitive call empty_8042 + popw %dx jnz a20_wait # A20 already on? + +# If A20 is still off, we need to go to the KBC. Set the +# "fast A20 gate" to its original value, since some smartass +# manufacturers have apparently decided to use A20M# as a GPIO! + movb %dl,%al + outb %al,$0x92 movb $0xD1, %al # command write outb %al, $0x64
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