Hi Wing/Okash

I know what OSI mode is supposed to deliver in theory – I just haven’t seen any compelling evidence of its benefit in practice. If you can share any evidence (even anecdotal) that would be great, although it’s not essential for these patches to proceed.

However, we are going to need some upstream platform(s) to exercise the new functionality. This can be a model platform, e.g. the Base FVP, not necessarily real hw. Are you able to at least get this running locally on Base FVP? I’m sure others can help with adding a config to the OpenCI.

Regards

Dan.

From: Wing Li <wingers@google.com>
Sent: 11 November 2022 18:34
To: Okash Khawaja <okash@google.com>
Cc: Dan Handley <Dan.Handley@arm.com>; tf-a@lists.trustedfirmware.org; tf-a-tests@lists.trustedfirmware.org
Subject: Re: [TF-A] Re: PSCI OS-initiated mode

Hi Dan,

Thanks for your feedback!

I've tested these patches with our platform, but have not tested with any upstream platforms. I added tests for the OS-initiated mode code path in TF-A-Tests [1] that we can run against upstream platforms to verify. I'm not sure how I can get a hold of an upstream platform board; it'd be much appreciated if perhaps maintainers of upstream platforms could help run the tests?

In theory, any platform that supports CPU_SUSPEND would be able to support both platform-coordinated mode and OS-initiated mode, since the power state coordination happens either in the PSCI library implementation or in an HLOS.

Wing

[1] https://review.trustedfirmware.org/c/TF-A/tf-a-tests/+/17684

On Fri, Nov 11, 2022 at 9:43 AM Okash Khawaja <okash@google.com> wrote:

Hi Dan,

The idea with OSI mode is that HLOS will have more awareness about
power sequences and hence will be able to optimise power usage better
(e.g. using heuristics) if it had more control. This means having HLOS
which contains right modules for a specific platform and specific use
case, if we want to do a power/perf comparison between OSI and
plat-coordinated modes.

On Fri, Nov 11, 2022 at 5:08 PM Dan Handley via TF-A
<tf-a@lists.trustedfirmware.org> wrote:
>
> Hi Wing
>
> Thanks for your contribution. Are there any upstream platforms that these patches have been tested with? If so, it would be good to have visibility of the sw stack under test. Ideally, there would be at least 1 platform that supported both platform-coordinated mode and OS-initiated mode, so that a fair power/performance comparison can be done.
>
>
>
> Regards
>
> Dan.
>
>
>
> From: Wing Li via TF-A <tf-a@lists.trustedfirmware.org>
> Sent: 10 November 2022 05:53
> To: tf-a@lists.trustedfirmware.org; tf-a-tests@lists.trustedfirmware.org
> Subject: [TF-A] PSCI OS-initiated mode
>
>
>
> Hi,
>
> The PSCI specification defines two different power state coordination modes for CPU_SUSPEND that can be used to put a core or a group of cores into a low-power state. These modes are the platform-coordinated mode (default) and the OS-initiated mode (optional). OS-initiated mode is currently not supported by TF-A, while both modes are supported by the Linux Kernel.
>
> Requesting reviews for the patches [1] adding support for OS-initiated mode in TF-A and the corresponding tests in TF-A-Tests. Any feedback and comments are much appreciated.
>
> Thanks in advance!
>
> Wing
>
> [1] https://review.trustedfirmware.org/q/topic:psci-osi
>
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