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

David P. Reed
2007-12-13T13:14:17Z

Perhaps what was meant is that ISA-tuned timings make little sense on
devices that are part of the chipset or on the PCI or PCI-X buses?

On the other hand, since we don't know in many cases whether the "_p"
was supposed to mean "the time it takes to execute an "out al,80h" on
whatever bus structure happens to be on whatever machine, the problem is
unsolvable.

Ranting about whether ISA/LPC is on what machines seems to be of little
value in contributing to a constructive solution.

It seems to me that in the long term, driver writers would do well to
think more clearly about the timings their devices require, when that is
possible. They are probably implementation dependent - depending on
the clock speed of the particular clock that is driving the particular
i/o device.

Then there's the social problem of a community development project -
which is to get people to tune their code but preserve its ability to
run on older and variant machines.

Alan Cox wrote:
>> Yes, it's now clear that all of this is so. Regrettably, it's used in
>> dozens of drivers, most having nothing to do with an ISA/LPC bus.
>>
>> If it really is specific to the ISA architecture, then it should only be
>> used in architecture specific code.
>>
>
> ISA/LPC is not architecture specific. In fact ISA/LPC bus components get
> everywhere because the PC market drives the cost per unit for those
> components down to nearly nothing.
>
>