Messages in this thread Patch in this message | | | Date | Tue, 28 Mar 2023 12:56:13 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] iommu/arm-smmu-v3: Fix event queue overflow acknowledgment |
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On Tue, Mar 28, 2023 at 07:13:52AM +0000, Krcka, Tomas wrote: > > > On 27. Mar 2023, at 14:12, Will Deacon <will@kernel.org> wrote: > > > > > > 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 > > Yes, we can, but then same applies for the priq as well, there we also write back > every time.
Sure, feel free to update both.
Will
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