On 2014-8-15 18:01, Catalin Marinas wrote:

Hanjun,

Hi Catalin,

On Fri, Aug 15, 2014 at 10:09:42AM +0100, Hanjun Guo wrote:

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On 2014-8-14 18:27, Catalin Marinas wrote:

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On Thu, Aug 14, 2014 at 04:21:25AM +0100, Hanjun Guo wrote:

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On 2014-8-14 7:41, Rafael J. Wysocki wrote:

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On Tuesday, August 12, 2014 07:23:47 PM Catalin Marinas wrote:

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If we consider ACPI unusable on ARM but we still want to start merging
patches, we should rather make the config option depend on BROKEN
(though if it is that unusable that no real platform can use it, I would
rather not merge it at all at this stage).

I agree here.

I would recommend creating a separate branch for that living outside of the
mainline kernel and merging it when there are real users.

Real users will coming soon, we already tested this patch set on real hardware
(ARM64 Juno platform),

I don't consider Juno a server platform ;) (but it's good enough for
development).

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and I think ARM64 server chips and platforms will show up before 3.18
is released.

That's what I've heard/seen. The questions I have are (a) whether
current ACPI patchset is enough to successfully run Linux on such
_hardware_ platform (maybe not fully optimised, for example just WFI
cpuidle) and (b) whether we still want to mandate a DT in the kernel for
such platforms.

For (a), this patch set is only for ARM64 core, not including platform
specific device drivers, it will be covered by the binding of _DSD or
explicit definition of PNP ID/ACPI ID(s).

So we go back to the discussions we had few months ago in Macau. I'm not
concerned about the core ARM and architected peripherals covered by ACPI
5.1 (as long as the current patches get positive technical review). But
I'm concerned about the additional bits needed for a real SoC like _DSD
definitions, how they get reviewed/accepted (or is it just the vendor's
problem?).

As the _DSD patch set sent out by Intel folks, _DSD definitions are just
DT definitions. To use _DSD or not, I think it depends on OEM use cases,
we can bring up Juno without _DSD (Graeme is working on that, still need
some time to clean up the code).

I think SBSA is too vague to guarantee a kernel image running on a
compliant platform without additional (vendor-specific) tweaks. So what
I asked for is (1) a document (guide) to define the strict set of ACPI
features and bindings needed for a real SoC and (2) proof that the
guidelines are enough for real hardware. I think we have (1) under
review with some good feedback so far. As for (2), we can probably only
discuss Juno openly. I think you could share the additional Juno patches
on this list so that reviewers can assess the suitability. If we deem
ACPI not (yet) suitable for Juno, is there other platform we could see
patches for?

Ok, we will send out all the patches for Juno in next version for review,
as mentioned above, we still need more time to clean up the code.

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Given the answer to (a) and what other features are needed, we may or
may not mandate (b). We were pretty clear few months ago that (b) is
still required but at the time we were only openly talking about ACPI
5.0 which was lacking many features. I think we need to revisit that
position based on how usable ACPI 5.1 for ARM (and current kernel
implementation) is. Would you mind elaborating what an ACPI-only
platform miss?

Do you mean something still missing? We still miss some features for
ARM in ACPI, but I think they are not critical, here is the list I can
remember:
- ITS for GICv3/4;
- SMMU support;
- CPU idle control.

I agree, these are not critical at this stage. But they only refer to
architected peripherals. Is there anything else missing for an SoC? Do
we need to define clocks?

No, I prefer not. As we discussed in this thread before, we don't need
clock definition if we use SBSA compatible UART on Juno.

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For ACPI 5.1, it fixes many problems for ARM:
- weak definition for GIC, so we introduce visualization, v2m and
  part of GICv3/4 (redistributors) support.
- No support for PSCI. Fix it to support PSCI 0.2+;
- Not support for Always-on timer and SBSA-L1 watchdog.

These are all good, that's why we shouldn't even talk about ACPI 5.0 in
the ARM context.

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- How to describe device properties, so _DSD is introduced for
  device probe.

For the last bullet, is there any review process (at least like what we
have for DT bindings)? On top of such process, do we have guidelines and
example code on how the Linux support should be implemented. As Olof
mentioned, should we see how the DT and ACPI probing paths work
together? I really think we should be very clear here and not let
vendors invent their own independent methods.

As said above, Intel folks provided some good examples for that, and
clarified a lot of things:

https://lkml.org/lkml/2014/8/17/10

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I would expect a new server platform designed with ACPI in mind to
require minimal SoC specific code, so we may only see a few patches
under drivers/ for such platforms adding ACPI-specific probing (possibly
new drivers as well if it's a new component).

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For this patch set, DT is the first class citizen at now:

a) We can always set CONFIG_ACPI as off in Kconfig, and use DT only;

Not just off but, based on maturity, depend on EXPERT.

Ok. And don't set ACPI default off (pass acpi=on to enable it)?

That's my view, just make it clear ACPI is experimental at the Kconfig
level because longer term we won't mandate SoCs to provide both DT and
ACPI tables.

I agree with you that if we set ACPI default off, firmware will always
pass acpi=on if they want to use ACPI, so I think it would be better
to depend on EXPERT instead.

Olof, is it ok to you too?

Thanks
Hanjun