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

From: David P. Reed
Date: Sun Dec 16 2007 - 18:07:33 EST


The process of safely making delicate changes here is beyond my responsibility as just a user - believe me, I'm not suggesting that a risky fix be put in .24. I can patch my own kernels, and I can even share an unofficial patch with others for now, or suggest that Fedora and Ubuntu add it to their downstream.

May I make a small suggestion, though. If the decision is a DMI-keyed switch from out-80 to udelay(2) gets put in, perhaps there should also be a way for people to test their own configuration for the underlying problem made available as a script. Though it is a "hack", all you need to freeze a problem system is to run a loop doing about 1000 "cat /dev/nvram > /dev/null" commands. If that leads to a freeze, one might ask to have the motherboard added to the DMI-key list.

H. Peter Anvin wrote:
Ingo Molnar wrote:
* H. Peter Anvin <hpa@xxxxxxxxx> wrote:

Pavel Machek wrote:
this is also something for v2.6.24 merging.
As much as I like this patch, I do not think it is suitable for
.24. Too risky, I'd say.

No kidding! We're talking about removing a hack that has been successful on thousands of pieces of hardware over 15 years because it
^----[*]
breaks ONE machine.

[*] "- none of which needs it anymore -"

there, fixed it for you ;-)

So lets keep this in perspective: this is a hack that only helps on a very low number of systems. (the PIT of one PII era chipset is known to be affected)

Yes, but the status quo has been *tested* on thousands of systems and is known to work. Thus, changing it puts things into unknown territory, even if only a small number of machines actually need the current configuration.

Heck, there are only a small number of 386/486 machines still in operation and being actively updated.

unfortunately this hack's side-effects are mis-used by an unknown number of drivers to mask PCI posting bugs. We want to figure out those bugs (safely and carefully) and we want to remove this hack from modern machines that dont need it. Doing anything else would be superstition.

anyway, we likely wont be doing anything about this in .24.

Again, 24 is "right out". 25 is a "maybe", IMO. Rene's fix could be an exception, since it is a DMI-keyed workaround for a specific machine and doesn't change behaviour in general.

-hpa

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