Re: [PATCH v8 09/12] iommu/arm-smmu-v3: Implement pm_runtime & system sleep ops

[Pranjal Shrivastava <praan@google.com>]

On Sun, Jun 07, 2026 at 03:30:00PM -0700, Daniel Mentz wrote:
> On Mon, Jun 1, 2026 at 2:59 PM Pranjal Shrivastava <praan@google.com> wrote:
> > +static int __maybe_unused arm_smmu_runtime_suspend(struct device *dev)
> > +{
> > +       struct arm_smmu_device *smmu = dev_get_drvdata(dev);
> > +       struct arm_smmu_cmdq *cmdq = &smmu->cmdq;
> > +       int timeout = ARM_SMMU_SUSPEND_TIMEOUT_US;
> > +       u32 enables, target;
> > +       int ret;
> > +
> > +       /* Abort all transactions before disable to avoid spurious bypass */
> > +       arm_smmu_update_gbpa(smmu, GBPA_ABORT, 0);
> > +
> > +       /* Disable the SMMU via CR0.EN and all queues except CMDQ */
> > +       enables = CR0_CMDQEN;
> > +       ret = arm_smmu_write_reg_sync(smmu, enables, ARM_SMMU_CR0, ARM_SMMU_CR0ACK);
> > +       if (ret) {
> > +               dev_err(smmu->dev, "failed to disable SMMU\n");
> > +               return ret;
> > +       }
> > +
> > +       /*
> > +        * At this point the SMMU is completely disabled and won't access
> > +        * any translation/config structures, even speculative accesses
> > +        * aren't performed as per the IHI0070 spec (section 6.3.9.6).
> > +        */
> > +
> > +       /* Mark the CMDQ to stop and get the target index before the stop */
> > +       target = atomic_fetch_or_relaxed(CMDQ_PROD_STOP_FLAG, &cmdq->q.llq.atomic.prod);
> 
> I'm wondering if we need the non-relaxed version of atomic_fetch_or()
> here to benefit from the barrier guarantees. Otherwise, how do you
> ensure that CMDQ_PROD_STOP_FLAG isn't set before SMMUEN is cleared?

Ack. I agree we need a non-relaxed version, I missed that the STOP_FLAG
is purely RAM & was focused on the _relaxed variants to keep things
ordered as all were MMIO. I'll drop the relaxed semantics with the
STOP_FLAG.

> 
> > +       target &= CMDQ_PROD_IDX_MASK;

Thanks,
Praan