linux-kernel - Re: [PATCH 0/1] Use PSCI OS initiated mode for sc7280

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Message-ID: <CAD=FV=UK9zyQ=Mg3BaVCwOGBG3G7rW2pdpMFtGptR88p8ce9kg@mail.gmail.com>
Date:   Mon, 27 Feb 2023 08:10:27 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Bjorn Andersson <andersson@...nel.org>
Cc:     Maulik Shah <quic_mkshah@...cinc.com>, ulf.hansson@...aro.org,
        swboyd@...omium.org, wingers@...gle.com,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_lsrao@...cinc.com, quic_rjendra@...cinc.com,
        Julius Werner <jwerner@...omium.org>
Subject: Re: [PATCH 0/1] Use PSCI OS initiated mode for sc7280

Hi,

On Mon, Feb 27, 2023 at 7:35 AM Bjorn Andersson <andersson@...nel.org> wrote:
>
> On Wed, Feb 15, 2023 at 12:46:48PM +0530, Maulik Shah wrote:
> > This change adds power-domains for cpuidle states to use PSCI OS
> > initiated mode for sc7280.
> >
> > This change depends on external project changes [1] & [2] which are under
> > review/discussion to add PSCI os-initiated support in Arm Trusted Firmware.
> >
> > I can update here once the dependency are in and change is ready to merge.
> >
>
> Please do, I will drop this from the queue for now.

I'm a bit confused about why we're doing this. There's always been a
question about exactly why we need OSI mode. As far as I can tell it
can't be for "correctness" reasons because we managed to ship sc7180
without OSI mode. ...so I guess somehow the argument is that OSI mode
is more performant in some cases? Are there actual numbers backing
this up, or is it all theoretical? Before making such a big change, it
would be good to actually understand what the motivation is and see
real data. This should be easy to collect since we currently have
things working without OSI and (presumably) you have OSI working. It
would also be good to document this motivation in the commit message
and/or cover letter.

-Doug