Re: [Patch v2] x86, ACPI, irq: Add a quirk to override SCI polarity for HyperV

[Thomas Gleixner <tglx@linutronix.de>]

On Thu, 20 Aug 2015, Jiang Liu wrote:
> On 2015/8/19 16:40, Thomas Gleixner wrote:
> > On Wed, 19 Aug 2015, Thomas Gleixner wrote:
> >> On Wed, 19 Aug 2015, Jiang Liu wrote:
> >>> On 2015/8/19 14:45, Rafael J. Wysocki wrote:
> >>>> Well, the regression at hand has just shown that the assertion in the
> >>>> changelog of that commit ("no need for for special treatment for GSI
> >>>> used by ACPI SCI") does not really hold.  So, if the only motivation
> >>>> for it was to get rid of one extra check in mp_unregister_gsi()
> >>>> (mp_register_gsi() still needs to check if it is dealing with the SCI
> >>>> anyway), I'd vote for reverting it.
> >>> Hi Rafael,
> >>> 	The motivation is to treat SCI as normal IOAPIC interrupt so
> >>> we could enforce stricter pin attribute checking. Now it does reveal
> >>> flaws in ACPI BIOS implementations, but we ran into trouble about how to
> >>> handle those flaws:(
> >>
> >> The intent of this change is entirely correct, though it seems that
> >> reality of ACPI is just different.
> >>
> >> To be on the safe side of things, I agree with Rafael that we should
> >> revert that patch instead of introducing a single platform quirk.
> > 
> > Jiang,
> > 
> > can you please prepare a revert patch for this?
> Hi Rafael and Thomas,
> 	I have tried to revert commit cd68f6bd53cf, but found
> it's not an easy task now.

That's what I feared

> 	When converting to hierarchical irqdomain, the IOAPIC
> internal and interfaces have changed much, and seems no easy
> way to revert cd68f6bd53cf. There may be three possible solutions
> here:
> 1) use quirk to correct SCI polarity, as the patch does.
> 2) change IOAPIC interfaces to provide a special way to
>    handle SCI interrupt.
> 3) change drivers/acpi/pci_link.c to penalize SCI IRQ so it
>    won't be used for PCI IRQ if SCI polarity conflicts with
>    PCI IRQ polarity.

Stupid question. Is the SCI polarity ever the opposite of PCI
polarity? I.e. is such a ACPI override valid at all? 

Thanks,

	tglx