Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64 with MCP51 laptops

H. Peter Anvin
2007-12-11T17:06:24Z

David P. Reed wrote:
> I do remind all that 0x80 is a BIOS-specific standard, and is per BIOS -
> other ports have been used in the history of the IBM PC family by some
> vendors, and some machines have used it for DMA port mapping!!

Correction: ALL machines use it for DMA port mapping. The port is
assigned to the legacy DMA controller, but performs no operation.
That's what makes it safe to write (NOT read!)

-hpa