New subject: Notes on Linaro Open Discussions meeting 4 Nov 2020

25 Nov 2020

      On Wed, Nov 25, 2020 at 4:01 PM Lorenzo Pieralisi via
Linaro-open-discussions linaro-open-discussions@op-lists.linaro.org wrote:
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On Wed, Nov 25, 2020 at 03:22:19PM +0000, Jonathan Cameron wrote:
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On Wed, 25 Nov 2020 13:58:38 +0000
Lorenzo Pieralisi lorenzo.pieralisi@arm.com wrote:
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On Wed, Nov 25, 2020 at 12:51:49PM +0000, Jonathan Cameron wrote:
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Is December 2nd confirmed as next session ? If possible 3PM GMT
works
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better for me; the NUMA topic raised by Jonathan is another
interesting
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topic for debate.
Just to check, which NUMA topic?
https://op-lists.linaro.org/pipermail/linaro-open-discussions/2020-November/...
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It would be useful (for me certainly) if you can give an update on
what's still pending in the items in the discussion above (eg it is
not clear what the "PCI fix" is) + how it is linked to CXL.
Sure, that should be a fairly short topic, but I'm happy to try to fill
in the gaps.
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@Mike, can you add "Generic initiators - pending items" to the agenda.
For the PCI 'fix'  it is this one that got applied and then reverted in
4.20 timeframe
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http://patchwork.ozlabs.org/project/linux-pci/patch/20180912152140.3676-2-Jo...
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I've not rebased or tested it recently so I'll check that it still
appears to be right
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before the call.
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The vCPU hotplug is also worth adding (even though I do not know what
was discussed at KVM forum).
I was just about to email about that one.  From our side, all that is
currently
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going on around vCPU Hotplug is a rebase.   At KVM forum Mark R kindly
offered
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to see if he could find out answers to a few open questions.  Perhaps
catch
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up with Mark, or see if he can make the call?
Ok, will catch up with him, it is probably better if I have some time
to do it (ie postpone the call for a week).
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Furthermore, I am keen on discussing this:
https://lore.kernel.org/linux-arm-kernel/20201123065410.1915-1-lushenming@hu...
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if the submitters are available, it would help to get some context in
relation to upstream discussions.
I've messaged lushenming so hopefully we can sort out something on that
front.
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Looks like finding a time next week is proving challenging.  If that
fails, perhaps we should try for the week after?
Yes we can, it would be easier to prepare the topics and find a suitable
day as well, next week it looks like it is challenging. It would also
give us some time to extend the invite.
Please let me know and apologies to Mike for all these emails to get it
organized.
No problem, as soon as it is confirmed we want to try for the following
week I can set up a poll to pick the day and hour
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Thanks,
Lorenzo
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Thanks,
Jonathan
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Thanks !
Lorenzo
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I've lost track of what we are talking about.
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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
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even though those require a bit of preparation so the sooner we
finalize
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the schedule the better.
Seems we have clashed with some internal Huawei activities so some
people who
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would normally be active are snowed under this week.
Jonathan
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Please let me know, thanks.
Lorenzo
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DT alignment. Don't want different solutions for each firmware

type.
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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.
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They support stall mode for SVA (spec violation)
Resistance from kernel maintainers to maintaining a white

list for any quirk. Fine to fix
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it once (JPB), but not to keep doing so.

Note that stall mode not yet supported at all (JPB to send

out this cycle).
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If longer term fix need add can't be done via PCISIG etc then

need to convince
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PCI and SMMU maintainers.   Noted that quirk is very little
code.
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Other SVA topics.
Mentioned virtual SVA (no actually problems just expressing

interest!)
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Would need Eric Auger, wasn't on topic list so Eric not on

call.
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AI: Nothing planned until after JPB has upstreamed stall mode.
Hard to have discussion before that.
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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.
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3 options:

MMIO / kernel driver.
PSCI via trusted firmware and system management controller.
ACPI (wrapping up an op region and SCMI)

Clarifications / discussions.

Vincent G: Power states, or voltage frequency of interest?

Ans Voltage Freq
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Considered SCMI?  Ans: Works only for DT as SCMI under ACPI

is wrapped up in AML
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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
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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.-
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Sudeep H Observed need to expose it via ACPI spec. (option 3

above).
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Sudeep H: Does PCI also need fine-grain control? We might

need to add to the spec.
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Sudeep H:  What are the requirements? gaohanjun: Now we just

frequency scaling.
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Jonathan C: Noted PCI power state is not enough.  It's

workload dependent.
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Sudeep H: We need to gather all the info, need to talk in

ASWG about DVFS
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Jonathan C:  For now direct control probably makes sense.

Whilst it would be nice to have
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a detailed enough system description in a standard way to
make general software that is a
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big spec job.

Jonathan C: Seems like true standard SW will not happen any

time soon.
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AI: RFC to the linux-pm / linux-acpi Rafael and those in this
discussion to ask about
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interest in adding per device DVFS to ACPI spec.  Possibly

pursue code first ACPI
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approach.

If I've miss listed or "volunteered" anyone for AIs they didn't
agree to then please
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correct that.
Thanks all for contributions. I for one found it a very useful
call!
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Jonathan
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-- 
Mike Holmes | Director, Foundation Technologies, Linaro
Mike.Holmes@linaro.org mike.holmes@linaro.org
 "Work should be fun and collaborative, the rest follows"

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

SVA

DVFS