> - The SMI handler in the BIOS masks the PIC interrupts. It reads the
> current mask (this is where the wrong value is obtained).
> At exit from SMI, it restores this wrong value to register 0x21.
> The SMI handler simply does not account for the fact that
> the PIC may be in polling mode when it reads register 0x21.
> We are right now trying a patched BIOS that does a dummy read
> on the PIC, before trying to obtain the mask from 0x21.
> This is an (almost) standard Phoenix BIOS, the IRQ masking code
> was definitely not changed by anyone at our company.
Why do you need to fiddle with the 8259A's IMR at all? What's wrong with
cli?
> Thus yes, the timer_ack code is actually (partly) responsible for
> our hang. I propose a patch for this below.
The current code is correct, written to 8259A's specs. I used original
ones ("8259A Programmable Interrupt Controller (8259A/8259A-2)", Intel's
order number 231468) as a reference to assure whatever happens is
well-specified and not an implementation-specific quirk. The SMI code is
broken for not being transparent (or for existing at all, but that's
another matter).
> We use normal ExtInt operation:
>
> Mar 12 16:51:30 pdb0374c kernel: ENABLING IO-APIC IRQs
> Mar 12 16:51:30 pdb0374c kernel: ...changing IO-APIC physical APIC ID to 2 ... ok.
> Mar 12 16:51:30 pdb0374c kernel: ...changing IO-APIC physical APIC ID to 3 ... ok.
> Mar 12 16:51:30 pdb0374c kernel: ..TIMER: vector=0x31 pin1=-1 pin2=0
> Mar 12 16:51:30 pdb0374c kernel: ...trying to set up timer (IRQ0) through the 8259A ...
> Mar 12 16:51:30 pdb0374c kernel: ..... (found pin 0) ...works.
That's not the normal mode -- that's the through-8259A mode workaround
designed originally for i82357 (ISP) based EISA systems. The chip
predates the APIC and does not make IRQ 0 from its internal 8254 core
available externally. I am actually very surprised to see new systems not
connecting IRQ 0 to the I/O APIC.
-- + Maciej W. Rozycki, Technical University of Gdansk, Poland + +--------------------------------------------------------------+ + e-mail: macro@ds2.pg.gda.pl, PGP key available +- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/