From: Nicolin Chen <nicolinc@nvidia.com>
To: Pranjal Shrivastava <praan@google.com>
Cc: <iommu@lists.linux.dev>, Will Deacon <will@kernel.org>,
Joerg Roedel <joro@8bytes.org>,
Robin Murphy <robin.murphy@arm.com>,
Jason Gunthorpe <jgg@ziepe.ca>,
Mostafa Saleh <smostafa@google.com>,
Daniel Mentz <danielmentz@google.com>,
Ashish Mhetre <amhetre@nvidia.com>,
<linux-arm-kernel@lists.infradead.org>,
Thomas Gleixner <tglx@kernel.org>, Radu Rendec <radu@rendec.net>,
Bjorn Helgaas <bhelgaas@google.com>, <linux-pci@vger.kernel.org>,
<linux-kernel@vger.kernel.org>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
<rafael@kernel.org>, "Danilo Krummrich" <dakr@kernel.org>,
<driver-core@lists.linux.dev>
Subject: Re: [PATCH v11 03/16] iommu/arm-smmu-v3: Add arm_smmu_drain_queue() helper
Date: Wed, 30 Sep 2026 11:24:21 -0700 [thread overview]
Message-ID: <ar1T1ecOPXb6JSPc@nvidia.com> (raw)
In-Reply-To: <20260929034510.2023173-4-praan@google.com>
On Tue, Sep 29, 2026 at 03:44:57AM +0000, Pranjal Shrivastava wrote:
> +/**
> + * 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/
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
next prev parent reply other threads:[~2026-09-30 18:24 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-29 3:44 [PATCH v11 00/16] iommu/arm-smmu-v3: Implement Runtime/System Sleep ops Pranjal Shrivastava
2026-09-29 3:44 ` [PATCH v11 01/16] iommu/arm-smmu-v3: Refactor arm_smmu_setup_irqs Pranjal Shrivastava
2026-09-29 3:59 ` sashiko-bot
2026-10-07 14:06 ` Will Deacon
2026-09-29 3:44 ` [PATCH v11 02/16] iommu/arm-smmu-v3: Add Q_POS() macro Pranjal Shrivastava
2026-09-29 4:01 ` sashiko-bot
2026-09-29 3:44 ` [PATCH v11 03/16] iommu/arm-smmu-v3: Add arm_smmu_drain_queue() helper Pranjal Shrivastava
2026-09-29 4:11 ` sashiko-bot
2026-09-30 18:24 ` Nicolin Chen [this message]
2026-09-30 20:17 ` Pranjal Shrivastava
2026-09-29 3:44 ` [PATCH v11 04/16] iommu/tegra241-cmdqv: Add a helper to drain VCMDQs Pranjal Shrivastava
2026-09-29 4:24 ` sashiko-bot
2026-09-29 3:44 ` [PATCH v11 05/16] iommu/arm-smmu-v3: Add a helper to drain cmd queues Pranjal Shrivastava
2026-09-29 4:31 ` sashiko-bot
2026-09-29 3:45 ` [PATCH v11 06/16] iommu/tegra241-cmdqv: Restore PROD and CONS after resume Pranjal Shrivastava
2026-09-29 4:42 ` sashiko-bot
2026-09-29 3:45 ` [PATCH v11 07/16] genirq/msi: Cache MSI message in irq_chip_write_msi_msg() Pranjal Shrivastava
2026-09-29 5:07 ` sashiko-bot
2026-09-29 3:45 ` [PATCH v11 08/16] genirq/msi: Provide msi_device_domain_restore_msi_msgs() Pranjal Shrivastava
2026-09-29 5:22 ` sashiko-bot
2026-09-29 3:45 ` [PATCH v11 09/16] iommu/arm-smmu-v3: Restore MSI config on resume Pranjal Shrivastava
2026-09-29 5:31 ` sashiko-bot
2026-10-07 14:07 ` Will Deacon
2026-09-29 3:45 ` [PATCH v11 10/16] iommu/arm-smmu-v3: Factor out arm_smmu_handle_gerror() Pranjal Shrivastava
2026-09-29 5:37 ` sashiko-bot
2026-09-30 18:34 ` Nicolin Chen
2026-09-30 20:00 ` Pranjal Shrivastava
2026-09-30 20:12 ` Nicolin Chen
2026-09-30 20:03 ` Pranjal Shrivastava
2026-10-07 14:07 ` Will Deacon
2026-09-29 3:45 ` [PATCH v11 11/16] iommu/arm-smmu-v3: Add CMDQ_PROD_STOP_FLAG to gate CMDQ submissions Pranjal Shrivastava
2026-09-29 5:55 ` sashiko-bot
2026-09-30 20:33 ` Nicolin Chen
2026-10-01 5:40 ` Pranjal Shrivastava
2026-10-01 18:03 ` Nicolin Chen
2026-10-02 16:47 ` Jason Gunthorpe
2026-10-02 21:11 ` Pranjal Shrivastava
2026-10-06 17:26 ` Nicolin Chen
2026-10-07 14:08 ` Will Deacon
2026-10-13 11:35 ` Robin Murphy
2026-09-29 3:45 ` [PATCH v11 12/16] iommu/tegra241-cmdqv: Add a helper to quiesce VCMDQs Pranjal Shrivastava
2026-09-29 6:05 ` sashiko-bot
2026-09-30 19:02 ` Nicolin Chen
2026-09-30 19:57 ` Pranjal Shrivastava
2026-09-30 20:03 ` Nicolin Chen
2026-09-29 3:45 ` [PATCH v11 13/16] iommu/arm-smmu-v3: Implement pm_runtime & system sleep ops Pranjal Shrivastava
2026-09-29 6:17 ` sashiko-bot
2026-10-01 20:22 ` Nicolin Chen
2026-10-07 14:08 ` Will Deacon
2026-09-29 3:45 ` [PATCH v11 14/16] iommu/arm-smmu-v3: Enable pm_runtime and setup devlinks Pranjal Shrivastava
2026-09-29 6:32 ` sashiko-bot
2026-09-29 3:45 ` [PATCH v11 15/16] iommu/arm-smmu-v3: Invoke pm_runtime before hw access Pranjal Shrivastava
2026-09-29 6:41 ` sashiko-bot
2026-09-29 3:45 ` [PATCH v11 16/16] iommu/arm-smmu-v3: Add KUnit unit tests for Runtime PM Pranjal Shrivastava
2026-09-29 6:48 ` sashiko-bot
2026-10-01 19:12 ` Nicolin Chen
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