From: Nicolin Chen <nicolinc@nvidia•com>
To: Pranjal Shrivastava <praan@google•com>
Cc: Jason Gunthorpe <jgg@nvidia•com>, <will@kernel•org>,
<robin.murphy@arm•com>, <joro@8bytes•org>, <bhelgaas@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 v6 3/3] iommu/arm-smmu-v3: Allow ATS to be always on
Date: Thu, 28 May 2026 11:20:35 -0700 [thread overview]
Message-ID: <ahiHc3y4wAxxtpLT@Asurada-Nvidia> (raw)
In-Reply-To: <ahiGIUDG2uvA6usM@google.com>
On Thu, May 28, 2026 at 06:14:57PM +0000, Pranjal Shrivastava wrote:
> On Thu, May 28, 2026 at 03:00:18PM -0300, Jason Gunthorpe wrote:
> > On Thu, May 28, 2026 at 04:32:23PM +0000, Pranjal Shrivastava wrote:
> > > On Thu, May 28, 2026 at 12:29:30PM -0300, Jason Gunthorpe wrote:
> > > > On Thu, May 28, 2026 at 03:24:40PM +0000, Pranjal Shrivastava wrote:
> > > >
> > > > > > + master->ats_always_on = true;
> > > > > > +
> > > > > > + return arm_smmu_alloc_cd_tables(master);
> > > > >
> > > > > Nit: I'm not sure if I'm getting this right, are we saying we *need* to
> > > > > allocate CDs for CXL.cache cases in the probe itself because STE.EATS
> > > > > requires Config=Translate with S1DSS in bypass?
> > > >
> > > > Yeah, basically.
> > > >
> > > > Effectively the ARM rules for enabling ATS and Bypass together require
> > > > a valid CD table pointer.
> > >
> > > Ack. But do we expect transactions before attach_dev? What'd happen if
> > > we don't allocate CDs here?
> >
> > It can be done at any point before a non-abort STE is formed.
> >
> > The core code pretty much does this immediately after probe so there
> > isn't much point in moving it later.
> >
>
> Right.. that's what I'm not understanding clearly, if the STE is Abort
> anyway during probe, why are we breaking the alloc-at-attach convention?
> Usually, we allocate CD tables in the first attach_dev call. Why does
> that not work here?
It would work in attach_dev(). I just felt cleaner to have it in
probe(), paired with arm_smmu_free_cd_tables() in the release().
Thanks
Nicolin
next prev parent reply other threads:[~2026-05-28 18:21 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-21 20:34 [PATCH v6 0/3] Allow ATS to be always on for certain ATS-capable devices Nicolin Chen
2026-05-21 20:34 ` [PATCH v6 1/3] PCI: Add pci_ats_required() for CXL.cache capable devices Nicolin Chen
2026-05-21 20:57 ` Bjorn Helgaas
2026-05-21 21:07 ` Nicolin Chen
2026-05-21 21:31 ` Bjorn Helgaas
2026-05-21 21:59 ` Nicolin Chen
2026-05-22 9:19 ` Yi Liu
2026-05-21 20:34 ` [PATCH v6 2/3] PCI: Allow ATS to be always on for pre-CXL devices Nicolin Chen
2026-05-22 9:17 ` Yi Liu
2026-05-21 20:34 ` [PATCH v6 3/3] iommu/arm-smmu-v3: Allow ATS to be always on Nicolin Chen
2026-05-28 15:24 ` Pranjal Shrivastava
2026-05-28 15:29 ` Jason Gunthorpe
2026-05-28 16:32 ` Pranjal Shrivastava
2026-05-28 18:00 ` Jason Gunthorpe
2026-05-28 18:14 ` Pranjal Shrivastava
2026-05-28 18:20 ` Nicolin Chen [this message]
2026-05-28 20:04 ` Jason Gunthorpe
2026-05-28 20:39 ` Pranjal Shrivastava
2026-05-28 7:35 ` [PATCH v6 0/3] Allow ATS to be always on for certain ATS-capable devices Jörg Rödel
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