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

Robin Murphy
2021-11-29T13:15:22Z

On 2021-11-29 10:55, Will Deacon wrote:
> Hi Thomas,
>
> On Sat, Nov 27, 2021 at 02:20:59AM +0100, Thomas Gleixner wrote:
>> Let the core code fiddle with the MSI descriptor retrieval.
>>
>> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>> ---
>> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 19 +++----------------
>> 1 file changed, 3 insertions(+), 16 deletions(-)
>>
>> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>> @@ -3154,7 +3154,6 @@ static void arm_smmu_write_msi_msg(struc
>>
>> static void arm_smmu_setup_msis(struct arm_smmu_device *smmu)
>> {
>> - struct msi_desc *desc;
>> int ret, nvec = ARM_SMMU_MAX_MSIS;
>> struct device *dev = smmu->dev;
>>
>> @@ -3182,21 +3181,9 @@ static void arm_smmu_setup_msis(struct a
>> return;
>> }
>>
>> - for_each_msi_entry(desc, dev) {
>> - switch (desc->msi_index) {
>> - case EVTQ_MSI_INDEX:
>> - smmu->evtq.q.irq = desc->irq;
>> - break;
>> - case GERROR_MSI_INDEX:
>> - smmu->gerr_irq = desc->irq;
>> - break;
>> - case PRIQ_MSI_INDEX:
>> - smmu->priq.q.irq = desc->irq;
>> - break;
>> - default: /* Unknown */
>> - continue;
>> - }
>> - }
>> + 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. 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?

Robin.