On 2021-11-29 10:55, Will Deacon wrote:

Hi Thomas,

On Sat, Nov 27, 2021 at 02:20:59AM +0100, Thomas Gleixner wrote:

quoted

Let the core code fiddle with the MSI descriptor retrieval.

Signed-off-by: Thomas Gleixner <redacted>
---
  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.