Messages in this thread | | | Subject | Re: [PATCH] x86/i8259: Work around buggy legacy PIC | From | "H. Peter Anvin" <> | Date | Fri, 14 May 2021 10:28:30 -0700 |
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On 5/14/21 9:12 AM, David Laight wrote: > > A more interesting probe would be: > - Write some value to register 1 - the mask. > - Write 9 to register zero (selects interrupt in service register). > - Read register 0 - should be zero since we aren't in as ISR. > - Read register 1 - should get the mask back. > You can also write 8 to register 0, reads then return the pending interrupts. > Their might be pending interrupts - so that value can't be checked. > > But if reads start returning the last written value you might only > have capacitors on the data bus.
What data bus? These things haven't been on a physical parallel bus for ages.
> The required initialisation registers are pretty fixed for the PC hardware. > But finding the values requires a bit of work. > > David
And you always risk activating new bugs.
Since this appears to be a specific platform advertising the wrong answer in firmware, this is better handled as a quirk.
-hpa
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