Re: [PATCH] x86_64: fix problems due to use of "outb" to port 80on some AMD64x2 laptops, etc.

[H. Peter Anvin]

David P. Reed wrote:
> Just a thought for a way to fix the "very early" timing needed to set up 
> udelay to work in a way that works on all machines.  Perhaps we haven't 
> exploited the BIOS enough:  The PC BIOS since the PC AT (286)  has 
> always had a standard "countdown timer" way to delay for n microseconds, 
> which as far as I know still works.   This can be used to measure the 
> speed of a delay loop, without using ANY in/out instructions directly 
> (the ones in the BIOS are presumably correctly delayed...).

If we enter from the 32-bit entrypoint, we already don't have access to 
the BIOS, though.

	-hpa
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/