[Linaro-open-discussions] Notes on Linaro Open Discussions meeting 4 Nov 2020

Mike Holmes mike.holmes at linaro.org
Mon Nov 23 16:44:56 UTC 2020


On Mon, Nov 23, 2020 at 3:13 PM Lorenzo Pieralisi via
Linaro-open-discussions <linaro-open-discussions at op-lists.linaro.org> wrote:

> On Thu, Nov 05, 2020 at 12:36:21PM +0000, Jonathan Cameron via
> Linaro-open-discussions wrote:
> >
> > Hi all,
> >
> > This is a fusion of Mike's notes and my own. Please add anything I
> missed!
> > People may well be misidentified (sorry about that).  Was very good
> active discussion.
> > Thanks to all involved and Mike in particular for organizing it and
> taking live notes.
> >
> > General request
> >
> >  - Slides for all topics next time to introduce topics as not everyone
> on call will have necessary
> >    background (and those that do might need reminding!)
> >    Hanjun is sending Mike his slides (uncore DVFS) to add to the
> collaborate page.
> >
> > IORT - Reserve memory regions (RMR)
> > ===================================
> >
> > * Shameer gave summary
> >  - IORT Revision E (
> https://developer.arm.com/documentation/den0049/latest/) introduced new
> node type.
> >  - A way to describe memory regions that should have unity mapping in
> the SMMU.
> >  - Use case is a PCIe RAID card that has FW that uses a pool of host
> memory (hidden from OS).
> >
> > * Status
> >  - Patches out for ACPICA
> >    - Question raised by ACPICA reviewers on whether spec is final
> >    - Spec appears final  (Lorenzo to check) but may be minor unrelated
> fix in doc to come (Sami).
> >  - Patches out for kernel on relevant lists.
> >    - Mail from Steven Price (Arm) - (Sami Mujawar who was on the call
> also involved) interested for EFI
> >      framebuffer use case.
> >
> > * Open questions
> >  - Equivalent from AMD has flag to indicate that unity mapping only
> needed until driver has taken over
> >    (end of kernel boot assumed).  Avoids and issue of holes in address
> space for VMs.
> >    - Huawei not raising this as a requirement, but Lorenzo observed
> interesting and deserves discussion.
> >  - Kexec interaction needs discussions. Steve looking at this an will
> bring to list.
> >  - Lorenzo brought up issue of IORT spec using PCI BDF (stream ID?)
> which may be reenumerated.
> >    - Noted x86 doesn't do this but ARM traditionally does.
> >    - There is a DSM that tells the kernel not to reenumerate the PCI bus
> which ACPI obeys.
> >    - Jonathan suggestion was potentially opportunity to cache original
> stream ID before doing the
> >      reenumeration in kernel.
> >    - Lorenzo observed we may need a universal solution for all OSes on
> this.
> >      Lorenzo took AI to go away and think about it before next call.
> >  - Stalling issues on patch?  Probably only Kexec though should be
> careful around possible future
> >    regressions on the BDF issue (not a blocker)
> >  - Related DT story.  Huawei server team not interested as no DT support
> and can't test.
> >    Lorenzo suggested looping in Thierry Reding and reference a patch set
> >    (probably
> https://lore.kernel.org/linux-iommu/20200904130000.691933-1-thierry.reding@gmail.com/#t
> )
> >    Huawei more than happy to have others add the DT support :)
> >
> > AI summary:
> > * Kexec discussion - on list.
> > * Use of BDF discussion - revisit here next time.
>
> I have an update on this topic and the RMR flags to free up IOVA.
>
> Is December 2nd confirmed as next session ?


It is if we have an agenda, which we now do, I added your topic as
confirmed.


> If possible 3PM GMT works
> better for me;


Linaro has a standing internal meeting with its members at 3.00 pm on
December 2nd,  how is 4.30 pm GMT or retain the 2.00 pm slot?


> the NUMA topic raised by Jonathan is another interesting
> topic for debate. Other than that we can slot in the topics that
> weren't discussed last time:
>
> https://collaborate.linaro.org/display/LOD/Linaro+Open+Discussions+Home
>
> even though those require a bit of preparation so the sooner we finalize
> the schedule the better.
>
> Please let me know, thanks.
>

I think we should prepare any topic slides and have the call, does anyone
have any additional agenda items?


>
> Lorenzo
>
> > * DT alignment. Don't want different solutions for each firmware type.
> > * Lorenzo / Sami to check IORT revision E is final.
> >
> > SVA
> > ===
> >
> > Zangfei gave summary:
> >  - Huawei has devices that are not PCIe but are presented as such.
> >  - They support stall mode for SVA (spec violation)
> >  - Resistance from kernel maintainers to maintaining a white list for
> any quirk. Fine to fix
> >    it once (JPB), but not to keep doing so.
> >  - Note that stall mode not yet supported at all (JPB to send out this
> cycle).
> >  - If longer term fix need add can't be done via PCISIG etc then need to
> convince
> >    PCI and SMMU maintainers.   Noted that quirk is very little code.
> >
> > * Other SVA topics.
> >   - Mentioned virtual SVA (no actually problems just expressing
> interest!)
> >   - Would need Eric Auger, wasn't on topic list so Eric not on call.
> >
> > AI: Nothing planned until after JPB has upstreamed stall mode. Hard to
> have discussion before that.
> >
> > DVFS
> > ====
> >
> > guohanjun
> >
> > Solutions exist for
> > * CPU DVFS (voltage + frequency scaling)
> > * PCIe device power states etc
> >
> > No standard way of controlling Uncore voltage and frequency for ACPI
> based systems.
> >
> > 3 options:
> > 1. MMIO / kernel driver.
> > 2. PSCI via trusted firmware and system management controller.
> > 3. ACPI (wrapping up an op region and SCMI)
> >
> > Clarifications / discussions.
> >  * Vincent G: Power states, or voltage frequency of interest? Ans
> Voltage Freq
> >  * Considered SCMI?  Ans: Works only for DT as SCMI under ACPI is
> wrapped up in AML
> >    so looks like an ACPI interface.
> >  * Sudeep H: Necessary to trace CPU freq?  Yes.
> >  * Sudeep H: Why not do it in firmware entirely?  Ans. Not just CPU.
> For example PCI device accessing
> >    memory may well need the ring bus to be fast.
> >  * Vincent G: Bandwidth affected?  Yes. VG: mobile does this by
> specifying a BW requirement (via SCMI.-
> >  * Sudeep H Observed need to expose it via ACPI spec. (option 3 above).
> >  * Sudeep H: Does PCI also need fine-grain control? We might need to add
> to the spec.
> >  * Sudeep H:  What are the requirements? gaohanjun: Now we just
> frequency scaling.
> >  * Jonathan C: Noted PCI power state is not enough.  It's workload
> dependent.
> >  * Sudeep H: We need to gather all the info, need to talk in ASWG about
> DVFS
> >  * Jonathan C:  For now direct control probably makes sense.  Whilst it
> would be nice to have
> >    a detailed enough system description in a standard way to make
> general software that is a
> >    big spec job.
> >  * Jonathan C: Seems like true standard SW will not happen any time soon.
> >
> > AI: RFC to the linux-pm / linux-acpi Rafael and those in this discussion
> to ask about
> >     interest in adding per device DVFS to ACPI spec.  Possibly pursue
> code first ACPI
> >     approach.
> >
> > If I've miss listed or "volunteered" anyone for AIs they didn't agree to
> then please
> > correct that.
> >
> > Thanks all for contributions. I for one found it a very useful call!
> >
> > Jonathan
> >
> >
> > --
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> > https://op-lists.linaro.org/mailman/listinfo/linaro-open-discussions
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>


-- 
Mike Holmes | Director, Foundation Technologies, Linaro
Mike.Holmes at linaro.org <mike.holmes at linaro.org>
 "Work should be fun and collaborative, the rest follows"


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