From: Jason Gunthorpe <jgg@nvidia•com>
To: Nicolin Chen <nicolinc@nvidia•com>
Cc: 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
Subject: Re: [PATCH v3 3/3] iommu/arm-smmu-v3: Allow ATS to be always on
Date: Mon, 30 Mar 2026 09:51:51 -0300 [thread overview]
Message-ID: <20260330125151.GK310919@nvidia.com> (raw)
In-Reply-To: <0e8d1ee1557c54943dd15ff836576de4c3aa58b6.1772833963.git.nicolinc@nvidia.com>
On Fri, Mar 06, 2026 at 03:41:17PM -0800, Nicolin Chen wrote:
> When a device's default substream attaches to an identity domain, the SMMU
> driver currently sets the device's STE between two modes:
>
> Mode 1: Cfg=Translate, S1DSS=Bypass, EATS=1
> Mode 2: Cfg=bypass (EATS is ignored by HW)
>
> When there is an active PASID (non-default substream), mode 1 is used. And
> when there is no PASID support or no active PASID, mode 2 is used.
>
> The driver will also downgrade an STE from mode 1 to mode 2, when the last
> active substream becomes inactive.
>
> However, there are PCIe devices that demand ATS to be always on. For these
> devices, their STEs have to use the mode 1 as HW ignores EATS with mode 2.
>
> Change the driver accordingly:
> - always use the mode 1
> - never downgrade to mode 2
> - allocate and retain a CD table (see note below)
>
> Note that these devices might not support PASID, i.e. doing non-PASID ATS.
> In such a case, the ssid_bits is set to 0. However, s1cdmax must be set to
> a !0 value in order to keep the S1DSS field effective. Thus, when a master
> requires ats_always_on, set its s1cdmax to minimal 1, meaning the CD table
> will have a dummy entry (SSID=1) that will be never used.
>
> Now, for these device, arm_smmu_cdtab_allocated() will always return true,
> v.s. false prior to this change. When its default substream is attached to
> an IDENTITY domain, its first CD is NULL in the table, which is a totally
> valid case. Thus, add "!master->ats_always_on" to the condition.
>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei•com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia•com>
> ---
> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 1 +
> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 72 ++++++++++++++++++---
> 2 files changed, 65 insertions(+), 8 deletions(-)
Reviewed-by: Jason Gunthorpe <jgg@nvidia•com>
Jason
next prev parent reply other threads:[~2026-03-30 12:52 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-06 23:41 [PATCH v3 0/3] Allow ATS to be always on for certain ATS-capable devices Nicolin Chen
2026-03-06 23:41 ` [PATCH v3 1/3] PCI: Allow ATS to be always on for CXL.cache capable devices Nicolin Chen
2026-03-08 20:49 ` Nirmoy Das
2026-03-08 20:53 ` Nirmoy Das
2026-03-09 11:48 ` Jonathan Cameron
2026-03-26 21:38 ` Bjorn Helgaas
2026-03-26 21:51 ` Jason Gunthorpe
2026-03-30 12:48 ` Jason Gunthorpe
2026-03-31 8:19 ` Tian, Kevin
2026-04-09 22:45 ` Nicolin Chen
2026-04-09 22:52 ` Jason Gunthorpe
2026-04-10 0:04 ` Nicolin Chen
2026-04-10 3:13 ` Tian, Kevin
2026-04-10 12:05 ` Jason Gunthorpe
2026-04-13 6:40 ` Tian, Kevin
2026-03-06 23:41 ` [PATCH v3 2/3] PCI: Allow ATS to be always on for pre-CXL devices Nicolin Chen
2026-03-08 20:50 ` Nirmoy Das
2026-03-08 20:54 ` Nirmoy Das
2026-03-09 11:50 ` Jonathan Cameron
2026-03-30 12:49 ` Jason Gunthorpe
2026-03-31 8:24 ` Tian, Kevin
2026-03-06 23:41 ` [PATCH v3 3/3] iommu/arm-smmu-v3: Allow ATS to be always on Nicolin Chen
2026-03-08 20:52 ` Nirmoy Das
2026-03-30 12:51 ` Jason Gunthorpe [this message]
2026-03-31 8:40 ` Tian, Kevin
2026-03-31 12:08 ` Jason Gunthorpe
2026-04-01 8:15 ` Tian, Kevin
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=20260330125151.GK310919@nvidia.com \
--to=jgg@nvidia$(echo .)com \
--cc=baolu.lu@linux$(echo .)intel.com \
--cc=bhelgaas@google$(echo .)com \
--cc=dan.j.williams@intel$(echo .)com \
--cc=iommu@lists$(echo .)linux.dev \
--cc=jonathan.cameron@huawei$(echo .)com \
--cc=joro@8bytes$(echo .)org \
--cc=kevin.tian@intel$(echo .)com \
--cc=linux-arm-kernel@lists$(echo .)infradead.org \
--cc=linux-cxl@vger$(echo .)kernel.org \
--cc=linux-kernel@vger$(echo .)kernel.org \
--cc=linux-pci@vger$(echo .)kernel.org \
--cc=miko.lenczewski@arm$(echo .)com \
--cc=nicolinc@nvidia$(echo .)com \
--cc=praan@google$(echo .)com \
--cc=robin.murphy@arm$(echo .)com \
--cc=vsethi@nvidia$(echo .)com \
--cc=will@kernel$(echo .)org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
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