Sean,
Sean V Kelley <sean.v.kelley@xxxxxxxxxxxxxxx> writes:
> I looked into it Thomas. The issue is as you suggested early in the
> thread. If an IRQ arrives at line N of a non-primary IO-APIC and that
> line is masked, a new IRQ is generated on the primary IO-APIC/PIC.
>
> The BIOS setting to address this forwarding is as above Disable INTx
> Route to PCH/ICH/SouthBridge. When this bit is set, local INTx messages
> received from the PCI-E ports are not routed to legacy PCH - they are
> either converted into MSI via the integrated I/OxAPIC (if the I/OxAPIC
> mask bit is clear in the appropriate entries) or cause no further
> action (when mask bit is set).
>
> This capability is tested and supported fully on Intel platforms.
Thanks for the confirmation.
> Once you get to SKX/CLX things change and integrated IOxAPICs in the
> IIO module convert legacy PCI Express interrupt messages into MSI
> interrupts directly. Beyond SKX/CLX there are no longer IOxAPICs in
> IIO. IOxAPIC is only in the PCH. Devices connected to the
> IIO will use native MSI/MSI-x mechanisms.
>
> The problem is with the absolute lack of useful documentation. That’s
> not acceptable.
Yeah.
> You recall the work Olaf and Stefan did at SuSE ten years ago (?) on
> boot irq quirks and the amount of research they had to do it learn
> about the behavior.[4]
Oh yes.
> From a Real-Time Linux perspective this is really important to me. As
> we get closer to fully mainlined we need to have this information
> readily available with greater usage of threaded irqs in combination
> with legacy interrupts on the older platforms.
>
> So I will ensure we actually create useful information pointing to this
> behavior either in kernel docs or online as in a white paper or both.
Great.
>> As we have already quirks in drivers/pci/quirks.c which handle the
>> same issue on older chipsets, we really should add one for these kind
>> of systems to avoid fiddling with the BIOS (which you can, but most
>> people cannot).
> Agreed, and I will follow-up with Kar Hin Ong to get them added.
Much appreciated.
Thanks,
tglx
