From: Jason Gunthorpe <jgg@nvidia.com>
To: "Dan Williams (nvidia)" <djbw@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: Fri, 1 May 2026 20:46:41 -0300 [thread overview]
Message-ID: <20260501234641.GB1381708@nvidia.com> (raw)
In-Reply-To: <69f536ed263dd_3291a910017@djbw-dev.notmuch>
On Fri, May 01, 2026 at 04:27:41PM -0700, Dan Williams (nvidia) wrote:
> You appear to be confusing Cache_Capable and Cache_Enabled.
>
> "8.2.1.3.1 DVSEC Flex Bus Port Capability" != "8.2.1.3.3 DVSEC Flex Bus Port Status"
>
> Cache_Capable is only a capability. To check that the device has
> actually trained the CXL.cache alternate protocol you need to look at
> the status register.
The capable is probably a reasonable choice here unless you are
confident the status will never change after the device is first
discovered? ATS is being set early in the boot sequence.
It is pretty safe to be over eager with the ATS enablement, less safe
to get it off when it needs to be on.
Jason
next prev parent reply other threads:[~2026-05-01 23:47 UTC|newest]
Thread overview: 12+ 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 [this message]
2026-05-02 0:19 ` Dan Williams (nvidia)
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
2026-04-27 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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