From: Saravana Kannan <saravanak@google.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: John Garry <john.garry@huawei.com>,
Jean-Philippe Brucker <jean-philippe@linaro.org>,
Bjorn Helgaas <bhelgaas@google.com>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>, Will Deacon <will@kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/7] iommu: Permit modular builds of ARM SMMU[v3] drivers
Date: Wed, 6 Nov 2019 22:11:55 -0800 [thread overview]
Message-ID: <CAGETcx8QYBfGOBNtUTR+Lq_g+bmBxMOe0q=3U5UxvVqi+640Xw@mail.gmail.com> (raw)
In-Reply-To: <7e2429ed-6b25-a452-5e4d-51a5195b872f@arm.com>
On Mon, Nov 4, 2019 at 5:29 AM Robin Murphy <robin.murphy@arm.com> wrote:
>
> On 04/11/2019 12:16, John Garry wrote:
> > On 01/11/2019 21:13, Saravana Kannan wrote:
> >> On Fri, Nov 1, 2019 at 3:28 AM John Garry <john.garry@huawei.com> wrote:
> >>>
> >>> On 31/10/2019 23:34, Saravana Kannan via iommu wrote:
> >>>> I looked into the iommu-map property and it shouldn't be too hard to
> >>>> add support for it. Looks like we can simply hold off on probing the
> >>>> root bridge device till all the iommus in its iommu-map are probed and
> >>>> we should be fine.
> >>>>
> >>>>> I'm also unsure about distro vendors agreeing to a mandatory kernel
> >>>>> parameter (of_devlink). Do you plan to eventually enable it by
> >>>>> default?
> >>>>>
> >>>>>> static const struct supplier_bindings of_supplier_bindings[] = {
> >>>>>> { .parse_prop = parse_clocks, },
> >>>>>> { .parse_prop = parse_interconnects, },
> >>>>>> { .parse_prop = parse_regulators, },
> >>>>>> + { .parse_prop = parse_iommus, },
> >>>>>> {},
> >>>>>> };
> >>>>>>
> >>>>>> I plan to upstream this pretty soon, but I have other patches in
> >>>>>> flight that touch the same file and I'm waiting for those to get
> >>>>>> accepted. I also want to clean up the code a bit to reduce some
> >>>>>> repetition before I add support for more bindings.
> >>>>> I'm also wondering about ACPI support.
> >>>> I'd love to add ACPI support too, but I have zero knowledge of ACPI.
> >>>> I'd be happy to help anyone who wants to add ACPI support that allows
> >>>> ACPI to add device links.
> >>>
> >>> If possible to add, that may be useful for remedying this:
> >>>
> >>> https://lore.kernel.org/linux-iommu/9625faf4-48ef-2dd3-d82f-931d9cf26976@huawei.com/
> >>>
> >>
> >> I'm happy that this change might fix that problem, but isn't the
> >> problem reported in that thread more to do with child devices getting
> >> added before the parent probes successfully? That doesn't make sense
> >> to me.
> >
> > So the pcieport device and then the child device are added in the PCI
> > scan, but only some time later do the device drivers probe for these
> > devices; so it's not that the that pcieport driver creates the child
> > device.
> >
> > The problem then occurs in that the ordering the of device driver probe
> > is such that we have this: pcieport probe + defer (as no IOMMU group
> > registered), SMMU probe (registers the IOMMU group), child device probe,
> > pcieport really probe.
> >
> > Can't the piceport driver not add its child devices before it
> >> probes successfully? Or more specifically, who adds the child devices
> >> of the pcieport before the pcieport itself probes?
> >
> > The devices are actually added in order pcieport, child device, but not
> > really probed in that same order, as above.
>
> Right, in short the fundamental problem is that of_iommu_configure() now
> does the wrong thing. Deferring probe of the entire host bridge/root
> complex based on "iommu-map" would indeed happen to solve the problem by
> brute force, I think, but could lead to a dependency cycle for PCI-based
> IOMMUs as Jean points out.
Sorry for the late reply. Got caught up on other work.
I didn't think the SMMU itself was PCI based in the example Jean gave.
I thought it just happened to be the case where the SMMU probes after
the pcieport but before the other children. If the SMMU itself is a
child of the pcieport, how can it be required for the parent to
function? How will suspend/resume even work?! I feel like I'm missing
some context wrt to PCI that everyone else seems to know (which isn't
surprising).
> I hope to have time this week to work a bit
> more on pulling of_iommu_configure() apart to fix it properly, after
> which of_devlink *should* only have to worry about the child devices
> themselves...
Worry about child devices in what sense? From a non-iommu perspective?
-Saravana
next prev parent reply other threads:[~2019-11-07 6:12 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-30 14:51 [PATCH 0/7] iommu: Permit modular builds of ARM SMMU[v3] drivers Will Deacon
2019-10-30 14:51 ` [PATCH 1/7] drivers/iommu: Export core IOMMU API symbols to permit modular drivers Will Deacon
2019-10-30 14:51 ` [PATCH 2/7] iommu/of: Request ACS from the PCI core when configuring IOMMU linkage Will Deacon
2019-10-30 14:51 ` [PATCH 3/7] PCI: Export pci_ats_disabled() as a GPL symbol to modules Will Deacon
2019-10-30 20:30 ` Bjorn Helgaas
2019-10-30 14:51 ` [PATCH 4/7] Revert "iommu/arm-smmu: Make arm-smmu-v3 explicitly non-modular" Will Deacon
2019-10-30 14:51 ` [PATCH 5/7] iommu/arm-smmu-v3: Allow building as a module Will Deacon
2019-10-30 19:31 ` Joerg Roedel
2019-10-31 15:42 ` Will Deacon
2019-11-04 19:15 ` Jean-Philippe Brucker
2019-11-08 14:54 ` Will Deacon
2019-11-05 12:15 ` Joerg Roedel
2019-11-08 11:03 ` Will Deacon
2019-10-30 14:51 ` [PATCH 6/7] Revert "iommu/arm-smmu: Make arm-smmu explicitly non-modular" Will Deacon
2019-10-30 23:09 ` Jordan Crouse
2019-10-31 12:03 ` Will Deacon
2019-10-31 15:32 ` Jordan Crouse
2019-10-30 14:51 ` [PATCH 7/7] iommu/arm-smmu: Allow building as a module Will Deacon
2019-10-30 15:22 ` Rob Herring
2019-10-30 15:26 ` Will Deacon
2019-10-30 15:33 ` Robin Murphy
2019-11-04 19:34 ` Isaac J. Manjarres
2019-11-07 12:48 ` Will Deacon
2019-10-30 15:35 ` [PATCH 0/7] iommu: Permit modular builds of ARM SMMU[v3] drivers Robin Murphy
2019-10-30 15:54 ` Will Deacon
2019-10-31 0:57 ` Saravana Kannan
2019-10-31 19:37 ` Jean-Philippe Brucker
2019-10-31 23:34 ` Saravana Kannan
2019-11-01 10:27 ` John Garry
2019-11-01 21:13 ` Saravana Kannan
2019-11-04 12:16 ` John Garry
2019-11-04 13:29 ` Robin Murphy
2019-11-07 6:11 ` Saravana Kannan [this message]
2019-11-07 9:13 ` Jean-Philippe Brucker
2019-11-07 6:02 ` Saravana Kannan
2019-11-01 11:41 ` Jean-Philippe Brucker
2019-11-01 12:28 ` Lorenzo Pieralisi
2019-11-01 21:26 ` Saravana Kannan
2019-11-04 11:43 ` Lorenzo Pieralisi
2019-11-07 5:55 ` Saravana Kannan
2019-11-01 17:21 ` Will Deacon
2019-11-04 7:54 ` Jean-Philippe Brucker
2019-11-07 6:16 ` Saravana Kannan
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