From: Saravana Kannan <firstname.lastname@example.org>
To: Lorenzo Pieralisi <email@example.com>
Cc: Jean-Philippe Brucker <firstname.lastname@example.org>,
Will Deacon <email@example.com>,
Bjorn Helgaas <firstname.lastname@example.org>,
Robin Murphy <email@example.com>
Subject: Re: [PATCH 0/7] iommu: Permit modular builds of ARM SMMU[v3] drivers
Date: Wed, 6 Nov 2019 21:55:50 -0800 [thread overview]
Message-ID: <CAGETcx_0kwQTjM2BkW__ux8kRvazR-PuX4Hcp4fP_97QRLSkTQ@mail.gmail.com> (raw)
On Mon, Nov 4, 2019 at 3:43 AM Lorenzo Pieralisi
> On Fri, Nov 01, 2019 at 02:26:05PM -0700, Saravana Kannan wrote:
> > On Fri, Nov 1, 2019 at 5:28 AM Lorenzo Pieralisi
> > <firstname.lastname@example.org> wrote:
> > >
> > > On Fri, Nov 01, 2019 at 12:41:48PM +0100, Jean-Philippe Brucker wrote:
> > >
> > > [...]
> > >
> > > > > > 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.
> > > >
> > > > It's not as generic as device-tree, each vendor has their own table to
> > > > describe the IOMMU topology. I don't see a nice way to transpose the
> > > > add_links() callback there. Links need to be created either in a common
> > > > path (iommu_probe_device()) or in the APCI IORT driver.
> > >
> > > We can create a generic stub that calls into respective firmware
> > > handling paths (eg iort_dma_setup() in acpi_dma_configure()).
> > >
> > > There are three arches booting with ACPI so stubbing it out in
> > > specific firmware handlers is not such a big deal, less generic
> > > sure, but not catastrophically bad.
> > Ok, good to know.
> > > Obviously this works for IOMMU masters links
> > It's unclear to me what you are referring to here and it's throwing me
> > off on the rest of the email.
> > Did you mean to say "IOMMU master's links"? As in the bus masters
> > whose accesses go through IOMMUs? And "links" as in device links?
> > OR
> > Do you mean device links from bus master devices to IOMMUs here?
> I meant associating endpoints devices to the IOMMU they are connected
> In DT you do it through "iommus", "iommu-map" properties, in ACPI
> it is arch specific, doable nonetheless through ACPI (IORT on ARM)
> static tables data.
> > > - for resources
> > > dependencies (eg power domains) it deserves some thought, keeping in
> > > mind that IOMMUs are static table entries in ACPI and not device objects
> > > so they are not even capable of expressing eg power resources and
> > > suchlike.
> > If you can reword this sentence for me with more context or split it
> > into separate sentences, I'd appreciate that very much. I'd help me
> > understand this better and allow me to try to help out.
> In ACPI (at least on ARM but on x86 I suspect that's the same story with
> the DMAR table) an SMMU is presented in FW as an entry in a static
> table (eg IORT on ARM). I noticed that your patch series takes into
> account for instance eg clock dependencies in DT; this way the OS knows
> the clock(s) the SMMU depends on to be activated.
> In ACPI there is not a notion of "clock" (hopefully - unless someone
> sneaked that in using _DSD properties) but rather every device in the
> ACPI namespace (which is part of tables containing code that needs the
> ACPI interpreter to be used such as SSDT/DSDT - it is AML code) has ACPI
> objects describing power resources (ie ACPI specification 6.3, 7.2).
> The SMMU, since it is not itself an ACPI object in the ACPI namespace
> but rather an entry in a static ACPI table (IORT on ARM), can't have
> PowerResource object in it which means that at the moment there is no
> way you can detect a dependency on other power resources to be ON to
> build the device links you require to sort out the probe dependencies,
> which I *assume* that's the reason why you require to detect
> clock dependencies in DT.
> Maybe it is not even needed at all but in case it is I was giving
> a heads-up to say that clocks (or rather an all encompassing "power
> resource" dependency) dependencies in ACPI to build an SMMU as
> a module are not straightforward and most certainly will require
> firmware specifications updates.
> *Hopefully* in the short term all you need to detect is how endpoint
> devices are connected to an IOMMU and build device links to describe
> that probe dependency, if we need to throw power management into
> the picture there is more work to be done.
> I hope that's clearer, if it is not please let me know and I will
> try to be more precise.
Thanks for the detailed explanation and context Lorenzo. I understand
it better now.
next prev parent reply other threads:[~2019-11-07 5:56 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
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 [this message]
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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