From: "Dan Williams (nvidia)" <djbw@kernel.org>
To: Jason Gunthorpe <jgg@nvidia.com>,
"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, 01 May 2026 17:19:05 -0700 [thread overview]
Message-ID: <69f542f92e36e_3291a910052@djbw-dev.notmuch> (raw)
In-Reply-To: <20260501234641.GB1381708@nvidia.com>
Jason Gunthorpe wrote:
> 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.
True, a reset could turn on CXL.cache. Ok, stick with what you have.
The present state of alternate protocol negotiation is still relevant
though for distinguishing CXL protocol errors from other PCIe AER
"internal" errors.
Need a bit of fixup work for that to refresh the status bit after reset.
next prev parent reply other threads:[~2026-05-02 0:19 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
2026-05-02 0:19 ` Dan Williams (nvidia) [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=69f542f92e36e_3291a910052@djbw-dev.notmuch \
--to=djbw@kernel.org \
--cc=baolu.lu@linux.intel.com \
--cc=bhelgaas@google.com \
--cc=dan.j.williams@intel.com \
--cc=iommu@lists.linux.dev \
--cc=jgg@nvidia.com \
--cc=jonathan.cameron@huawei.com \
--cc=joro@8bytes.org \
--cc=kevin.tian@intel.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-cxl@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pci@vger.kernel.org \
--cc=miko.lenczewski@arm.com \
--cc=nicolinc@nvidia.com \
--cc=nirmoyd@nvidia.com \
--cc=praan@google.com \
--cc=robin.murphy@arm.com \
--cc=vsethi@nvidia.com \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox