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DateWed, 08 Jan 2003 11:48:29 -0800
From"H. Peter Anvin" <>
SubjectRe: tenth post about PCI code, need help
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Richard B. Johnson wrote:
On 8 Jan 2003, H. Peter Anvin wrote:


Followup to: <Pine.LNX.3.95.1030108132812.28791A-100000@chaos.analogic.com> By author: "Richard B. Johnson" <root@chaos.analogic.com> In newsgroup: linux.dev.kernel

The problem is that he's discovered something that's not supposed to be in the code. Only 32-bit accesses are supposed to be made to the PCI controller ports. He has discovered that somebody has made some 8-bit accesses that will not become configuration 'transactions' because they are not 32 bits.


Right. That's what the code is checking for.

-hpa

Somebody is very lucky the designer of the bus interface state-machine let him get away with it. This is a borderline "insane instruction" that could, on some (future?) machine, require a power-off to recover. This is NotGood(tm). It's like testing a fuse by shorting out a circuit. If it works, the circuit no longer works. If I doesn't, the circuit no longer works. Some things should not be tested.


If so, we will get an bug report rather than mysterious strange behaviour. This is a good thing. (Amusingly enough, exactly this code in the Linux kernel actually found a bug in one of the very early versions of the Transmeta northbridge. It was fixed in firmware.)
-hpa


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