[PATCH v8 02/12] iommu/arm-smmu-v3: Add a helper to drain cmd queues

[Daniel Mentz]

On Mon, Jun 1, 2026 at 2:59 PM Pranjal Shrivastava <praan at google.com> wrote:
> +static int arm_smmu_drain_queues(struct arm_smmu_device *smmu)
> +{
> +       int ret;
> +
> +       /*
> +        * Since this is only called from the suspend callback where
> +        * exclusive access is ensured as CMDQ_PROD_STOP_FLAG blocks new
> +        * command submissions to the cmdq, we can skip the cmdq locking.
> +        */

>From what I understand, the purpose of this lock is to ensure that
only one thread updates smmu->cmdq.q.cons. The flag
CMDQ_PROD_STOP_FLAG might block new threads from submitting commands
to the command queue. However, other threads might have already passed
that point and are about to update smmu->cmdq.q.cons. Hence, this
assumption might not be safe.

> +       ret = arm_smmu_queue_poll_until_empty(smmu, &smmu->cmdq.q);
> +
> +       return ret;
> +}