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 1/3] PCI: Allow ATS to be always on for CXL.cache capable devices
Date: Wed, 20 May 2026 14:56:06 -0300 [thread overview]
Message-ID: <20260520175606.GB3602937@nvidia.com> (raw)
In-Reply-To: <20260520174758.GA66039@bhelgaas>
On Wed, May 20, 2026 at 12:47:58PM -0500, Bjorn Helgaas wrote:
> I don't know enough about CXL to know what's behind the ATS
> requirement. It sounds like it's more than a simple performance
> optimization. If you happen to know the reason, it might be worth
> a short comment about that too.
At the core of this is underlying physical interconnect protocols that
only work with translated addresses.
Ie CXL.cache only has a definition for translated physical in its
protocol spec. The use of true physical only is due to the cache
coherence shootdown protocol..
It is why I suggested 'pci_translated_required()' earlier, there are a
few more than CXl.cache why a device might need translated physical
addresses only.
ATS is the only way for a device to get those addresses, so
ats_required is fine too, but it sort of glosses over what is driving
it.
Jason
next prev parent reply other threads:[~2026-05-20 17:56 UTC|newest]
Thread overview: 30+ 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 [this message]
2026-05-20 13:12 ` Yi Liu
2026-05-20 14:34 ` Jason Gunthorpe
2026-05-21 7:31 ` Yi Liu
2026-05-21 13:05 ` Jason Gunthorpe
2026-05-22 9:18 ` Yi Liu
2026-05-25 6:58 ` Tian, Kevin
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
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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