From: Nicolin Chen <nicolinc@nvidia•com>
To: Pranjal Shrivastava <praan@google•com>
Cc: <iommu@lists•linux.dev>, <linux-pci@vger•kernel.org>,
<linux-arm-kernel@lists•infradead.org>,
<linux-kernel@vger•kernel.org>, "Joerg Roedel" <joro@8bytes•org>,
Will Deacon <will@kernel•org>,
Bjorn Helgaas <bhelgaas@google•com>,
David Woodhouse <dwmw2@infradead•org>,
Lu Baolu <baolu.lu@linux•intel.com>,
Robin Murphy <robin.murphy@arm•com>,
"Suravee Suthikulpanit" <suravee.suthikulpanit@amd•com>,
Jason Gunthorpe <jgg@ziepe•ca>,
David Matlack <dmatlack@google•com>,
Samiullah Khawaja <skhawaja@google•com>,
Daniel Mentz <danielmentz@google•com>,
Pasha Tatashin <pasha.tatashin@soleen•com>,
Mostafa Saleh <smostafa@google•com>
Subject: Re: [PATCH v4 3/5] iommu/arm-smmu-v3: Fix ATS state tracking
Date: Mon, 25 May 2026 13:05:36 -0700 [thread overview]
Message-ID: <ahSrkOv+4QZWrcJq@Asurada-Nvidia> (raw)
In-Reply-To: <20260525184347.4059549-4-praan@google.com>
On Mon, May 25, 2026 at 06:43:45PM +0000, Pranjal Shrivastava wrote:
> @@ -3065,8 +3065,14 @@ static void arm_smmu_enable_ats(struct arm_smmu_master *master)
> * ATC invalidation of PASID 0 causes the entire ATC to be flushed.
> */
> arm_smmu_atc_inv_master(master, IOMMU_NO_PASID);
> - if (pci_enable_ats(pdev, stu))
> - dev_err(master->dev, "Failed to enable ATS (STU %zu)\n", stu);
> +
> + /*
> + * Any failure at this point is a kernel bug. pci_ats_supported()
> + * and pci_prepare_ats() have already verified the hardware capability
> + * and programmed the STU. Thus, pci_enable_ats() should not fail here.
Nits:
- WARN usually indicates a kernel bug already.
- pci_prepare_ats() covers pci_ats_supported().
/*
* As pci_prepare_ats() have already verified the hardware capability
* and programmed the STE, pci_enable_ats() should not fail here.
*/
> @@ -4264,9 +4270,16 @@ static struct iommu_device *arm_smmu_probe_device(struct device *dev)
> master->stall_enabled = true;
>
> if (dev_is_pci(dev)) {
> - unsigned int stu = __ffs(smmu->pgsize_bitmap);
> + struct pci_dev *pdev = to_pci_dev(dev);
>
> - pci_prepare_ats(to_pci_dev(dev), stu);
> + if (pci_ats_supported(pdev)) {
> + unsigned int stu = __ffs(smmu->pgsize_bitmap);
> + int ret;
> +
> + ret = pci_prepare_ats(pdev, stu);
> + if (ret)
> + return ERR_PTR(ret);
> + }
Again, pci_prepare_ats() covers pci_ats_supported(). So, the check
is redundant. Instead, it should check arm_smmu_ats_supported().
By the way, this would conflict into my series:
https://lore.kernel.org/linux-iommu/18bb6f421b3be891caa8f1fb50f3a4d56b52d5be.1779392420.git.nicolinc@nvidia.com/
It would be nicer to have an arm_smmu_master_prepare_ats() so that
both series would have a common ground; mine would be just adding
some additional lines if your series goes in first.
Thanks
Nicolin
next prev parent reply other threads:[~2026-05-25 20:06 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-25 18:43 [PATCH v4 0/5] iommu: Standardize ATS robustness and state tracking Pranjal Shrivastava
2026-05-25 18:43 ` [PATCH v4 1/5] PCI/ATS: Ensure pci_ats_supported() is PF-aware for VFs Pranjal Shrivastava
2026-05-25 19:42 ` Nicolin Chen
2026-05-25 18:43 ` [PATCH v4 2/5] PCI/ATS: Validate STU for VFs in pci_prepare_ats() Pranjal Shrivastava
2026-05-25 19:46 ` Nicolin Chen
2026-05-28 20:27 ` Pranjal Shrivastava
2026-05-25 18:43 ` [PATCH v4 3/5] iommu/arm-smmu-v3: Fix ATS state tracking Pranjal Shrivastava
2026-05-25 20:05 ` Nicolin Chen [this message]
2026-05-25 20:30 ` Pranjal Shrivastava
2026-05-25 20:40 ` Nicolin Chen
2026-05-25 18:43 ` [PATCH v4 4/5] iommu/vt-d: Fail probe on ATS configuration failure Pranjal Shrivastava
2026-05-25 18:43 ` [PATCH v4 5/5] iommu/amd: " Pranjal Shrivastava
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