From: Jason Gunthorpe <jgg@nvidia.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: Nicolin Chen <nicolinc@nvidia.com>,
will@kernel.org, robin.murphy@arm.com, bhelgaas@google.com,
joro@8bytes.org, praan@google.com, baolu.lu@linux.intel.com,
kevin.tian@intel.com, miko.lenczewski@arm.com,
linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev,
linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
dan.j.williams@intel.com, jonathan.cameron@huawei.com,
vsethi@nvidia.com, linux-cxl@vger.kernel.org, nirmoyd@nvidia.com
Subject: Re: [PATCH v4 2/3] PCI: Allow ATS to be always on for pre-CXL devices
Date: Wed, 20 May 2026 14:53:04 -0300 [thread overview]
Message-ID: <20260520175304.GA3602937@nvidia.com> (raw)
In-Reply-To: <20260520175026.GA67027@bhelgaas>
On Wed, May 20, 2026 at 12:50:26PM -0500, Bjorn Helgaas wrote:
> On Sun, Apr 26, 2026 at 10:54:01PM -0700, Nicolin Chen wrote:
> > Some NVIDIA GPU/NIC devices, though they don't implement CXL config space,
> > have many CXL-like properties. Call this kind "pre-CXL".
> >
> > Similar to CXL.cache capability, these pre-CXL devices also require the ATS
> > function even when their RIDs are IOMMU bypassed, i.e. keep ATS "always on"
> > v.s. "on demand" when a non-zero PASID line gets enabled in SVA use cases.
> > ...
>
> > +/* Some pre-CXL devices require ATS when it is IOMMU-bypassed */
>
> I guess these devices are purely PCIe, with no actual CXL
> transactions, so a hint here about what leads to the ATS requirement
> would be useful.
Not quite, they are not actually "real" PCIe devices, these are
devices that present to the system as PCIe, can issue CXL like .cache
operations and don't use PCIe electrical.
Jason
next prev parent reply other threads:[~2026-05-20 17:53 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-27 5:53 [PATCH v4 0/3] Allow ATS to be always on for certain ATS-capable devices Nicolin Chen
2026-04-27 5:54 ` [PATCH v4 1/3] PCI: Allow ATS to be always on for CXL.cache capable devices Nicolin Chen
2026-04-27 16:31 ` Dave Jiang
2026-04-30 21:41 ` Dan Williams (nvidia)
2026-04-30 23:28 ` Nicolin Chen
2026-05-01 23:27 ` Dan Williams (nvidia)
2026-05-01 23:46 ` Jason Gunthorpe
2026-05-02 0:19 ` Dan Williams (nvidia)
2026-05-19 19:36 ` Bjorn Helgaas
2026-05-19 22:23 ` Jason Gunthorpe
2026-05-19 23:48 ` Bjorn Helgaas
2026-05-20 0:05 ` Jason Gunthorpe
2026-05-20 1:04 ` Nicolin Chen
2026-05-20 14:20 ` Jason Gunthorpe
2026-05-20 17:29 ` Nicolin Chen
2026-05-20 17:47 ` Bjorn Helgaas
2026-05-20 17:56 ` Jason Gunthorpe
2026-05-20 13:12 ` Yi Liu
2026-05-20 14:34 ` Jason Gunthorpe
2026-04-27 5:54 ` [PATCH v4 2/3] PCI: Allow ATS to be always on for pre-CXL devices Nicolin Chen
2026-04-27 16:32 ` Dave Jiang
2026-05-20 13:12 ` Yi Liu
2026-05-20 17:50 ` Bjorn Helgaas
2026-05-20 17:53 ` Jason Gunthorpe [this message]
2026-04-27 5:54 ` [PATCH v4 3/3] iommu/arm-smmu-v3: Allow ATS to be always on Nicolin Chen
2026-04-27 16:37 ` Dave Jiang
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