Re: [PATCH v11 03/16] iommu/arm-smmu-v3: Add arm_smmu_drain_queue() helper
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From: Nicolin Chen <hidden>
Date: 2026-09-30 18:24:58
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driver-core, linux-iommu, linux-pci, lkml
On Tue, Sep 29, 2026 at 03:44:57AM +0000, Pranjal Shrivastava wrote:
quoted hunk ↗ jump to hunk
+/** + * arm_smmu_drain_queue - Drain an SMMU queue + * @smmu: the SMMU device + * @q: the queue to drain + * @until_empty: target selection + * + * With @until_empty == true (for CMDQ), exit once the queue is observed empty: + * + * cons0 cons prod + * | | | + * ---+###################+=====================+=============+---> + * |<--------- undrained==0? --------->|
Jason gave some remarks against this API: https://lore.kernel.org/linux-iommu/179018862538.3334538.17643821143626392419.b4-review@b4/ (local) So, my PRI series would drop this patch. I suspect that it still has some value for the RPM/CMDQ case, compared to a busy-waiting alternative. Yet, it probably should be simplified for CMDQ case only. In RPM case, the "prod" would be fixed/stable right? IOW, there should be no new commands added to the cmdq, so it only needs to wait for cons == prod? Nicolin