Messages in this thread Patch in this message | | | Date | Mon, 27 Mar 2023 13:12:34 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] iommu/arm-smmu-v3: Fix event queue overflow acknowledgment |
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On Wed, Mar 08, 2023 at 09:20:47AM +0000, Tomas Krcka wrote: > When an overflow occurs in the event queue, the SMMU toggles overflow > flag OVFLG in the PROD register. > The evtq thread is supposed to acknowledge the overflow flag by toggling > flag OVACKFLG in the CONS register, otherwise the overflow condition is > still active (OVFLG != OVACKFLG). > > Currently the acknowledge register is toggled after clearing the event > queue but is never propagated to the hardware. It would be done next > time when executing evtq thread. > > The SMMU still adds elements to the queue when the overflow condition is > active but any subsequent overflow information after clearing the event > queue will be lost. > > This change keeps the SMMU in sync as it's expected by design. > > Signed-off-by: Tomas Krcka <krckatom@amazon.de> > Suggested-by: KarimAllah Ahmed <karahmed@amazon.de> > --- > drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > index f2425b0f0cd6..acc1ff5ff69b 100644 > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > @@ -1579,6 +1579,7 @@ static irqreturn_t arm_smmu_evtq_thread(int irq, void *dev) > /* Sync our overflow flag, as we believe we're up to speed */ > llq->cons = Q_OVF(llq->prod) | Q_WRP(llq, llq->cons) | > Q_IDX(llq, llq->cons); > + queue_sync_cons_out(q); > return IRQ_HANDLED; > }
I think I probably did mean to have something like this, but can we only do the actual h/w update if overflow has occurred? Otherwise I think we're pointlessly writing back the same value most of the time.
Will
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