Re: [patch 33/37] iommu/arm-smmu-v3: Use msi_get_virq()

Thomas Gleixner
2021-11-29T14:44:19Z

On Mon, Nov 29 2021 at 13:13, Robin Murphy wrote:
> On 2021-11-29 10:55, Will Deacon wrote:
>>> - }
>>> + smmu->evtq.q.irq = msi_get_virq(dev, EVTQ_MSI_INDEX);
>>> + smmu->gerr_irq = msi_get_virq(dev, GERROR_MSI_INDEX);
>>> + smmu->priq.q.irq = msi_get_virq(dev, PRIQ_MSI_INDEX);
>>
>> Prviously, if retrieval of the MSI failed then we'd fall back to wired
>> interrupts. Now, I think we'll clobber the interrupt with 0 instead. Can
>> we make the assignments to smmu->*irq here conditional on the MSI being
>> valid, please?
>
> I was just looking at that too, but reached the conclusion that it's
> probably OK, since consumption of this value later is gated on
> ARM_SMMU_FEAT_PRI, so the fact that it changes from 0 to an error value
> in the absence of PRI should make no practical difference.

It's actually 0 when the vector cannot be found.

> If we don't have MSIs at all, we'd presumably still fail earlier
> either at the dev->msi_domain check or upon trying to allocate the
> vectors, so we'll still fall back to any previously-set wired values
> before getting here. The only remaining case is if we've
> *successfully* allocated the expected number of vectors yet are then
> somehow unable to retrieve one or more of them - presumably the system
> has to be massively borked for that to happen, at which point do we
> really want to bother trying to reason about anything?

Probably not. At that point something is going to explode sooner than
later in colorful ways.

Thanks,

tglx