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Date:   Thu, 30 Mar 2023 14:27:02 +0300
From:   Abel Vesa <abel.vesa@linaro.org>
To:     Saravana Kannan <saravanak@google.com>,
        Ulf Hansson <ulf.hansson@linaro.org>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Kevin Hilman <khilman@kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Pavel Machek <pavel@ucw.cz>, Len Brown <len.brown@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Andy Gross <agross@kernel.org>,
        Konrad Dybcio <konrad.dybcio@linaro.org>,
        Mike Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>, linux-pm@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-arm-msm@vger.kernel.org, linux-clk@vger.kernel.org,
        Doug Anderson <dianders@chromium.org>,
        Matthias Kaehlcke <mka@chromium.org>,
        Android Kernel Team <kernel-team@android.com>
Subject: Re: [PATCH v3 0/4] Allow genpd providers to power off domains on
 sync state
Message-ID: <ZCVyBuKMvDV0gQPW@linaro.org>
References: <20230327193829.3756640-1-abel.vesa@linaro.org>
 <CAGETcx9f1p2esfyzyfU04EAB1FXh=d9-U81DaGyZNjL_Vti3oQ@mail.gmail.com>
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On 23-03-27 17:17:28, Saravana Kannan wrote:
> On Mon, Mar 27, 2023 at 12:38 PM Abel Vesa <abel.vesa@linaro.org> wrote:
> >
> > There have been already a couple of tries to make the genpd "disable
> > unused" late initcall skip the powering off of domains that might be
> > needed until later on (i.e. until some consumer probes). The conclusion
> > was that the provider could return -EBUSY from the power_off callback
> > until the provider's sync state has been reached. This patch series tries
> > to provide a proof-of-concept that is working on Qualcomm platforms.
> 
> I'm giving my thoughts in the cover letter instead of spreading it
> around all the patches so that there's context between the comments.
> 
> 1) Why can't all the logic in this patch series be implemented at the
> framework level? And then allow the drivers to opt into this behavior
> by setting the sync_state() callback.
> 
> That way, you can land it only for QC drivers by setting up
> sync_state() callback only for QC drivers, but actually have the same
> code function correctly for non-QC drivers too. And then once we have
> this functionality working properly for QC drivers for one kernel
> version (or two), we'll just have the framework set the device's
> driver's sync_state() if it doesn't have one already.

I think Ulf has already NACK'ed that approach here:
[1] https://lore.kernel.org/lkml/CAPDyKFon35wcQ+5kx3QZb-awN_S_q8y1Sir-G+GoxkCvpN=iiA@mail.gmail.com/

And suggested this new approach that this patch series proposes.
(Unless I missunderstood his point)

> 
> 2) sync_state() is not just about power on/off. It's also about the
> power domain level. Can you handle that too please?

Well, this patchset only tries to delay the disabling of unused power
domains until all consumers have had a chance to probe. So we use sync
state only to queue up a power-off request to make sure those unused
ones get disabled.

> 
> 3) In your GDSC drivers, it's not clear to me if you are preventing
> power off until sync_state() only for GDSCs that were already on at
> boot. So if an off-at-boot GDSC gets turned on, and then you attempt
> to turn it off before all its consumers have probed, it'll fail to
> power it off even though that wasn't necessary?

I think we can circumvent looking at a GDSC by knowing it there was ever
a power on request since boot. I'll try to come up with something in the
new version.

> 
> 4) The returning -EBUSY when a power off is attempted seems to be
> quite wasteful. The framework will go through the whole sequence of
> trying to power down, send the notifications and then fail and then
> send the undo notifications. Combined with point (2) I think this can
> be handled better at the aggregation level in the framework to avoid
> even going that far into the power off sequence.

Again, have a look at [1] (above).

Ulf, any thoughts on this 4th point?

> 
> -Saravana
> 
> >
> > I've been doing extensive testing on SM8450, but I've also spinned this
> > on my X13s (SC8280XP). Both patches that add the sync state callback to
> > the SC8280XP and SM8450 are here to provide context. Once we agree on
> > the form, I intend to add the sync state callback to all gdsc providers.
> >
> > Currently, some of the gdsc providers might not reach sync state due to
> > list of consumers not probing yet (or at all). The sync state can be
> > enforced by writing 1 to the state_synced sysfs attribute of the
> > provider, thanks to Saravana's commit [1] which has been already merged.
> >
> > [1] https://lore.kernel.org/r/20230304005355.746421-3-saravanak@google.com
> >
> > V2 (RFC) of this patchset was here:
> > https://lore.kernel.org/all/20230320134217.1685781-1-abel.vesa@linaro.org/
> >
> > Changes since v2:
> >  * renamed genpd_queue_power_off_work to pm_genpd_queue_power_off and added
> >    comment about its purpose w.r.t. it being exported.
> >  * added the qcom_cc generic sync state callback to all providers that
> >    register GDSCs, instead of SM8450 and SC8280XP
> >
> > Changes since v1:
> >  * Added the qcom_cc sync state callback which calls in turn the gdsc one
> >  * dropped extra semicolon from pm_domain.h
> >
> > Abel Vesa (4):
> >   PM: domains: Allow power off queuing from providers
> >   soc: qcom: rpmhpd: Do proper power off when state synced
> >   clk: qcom: gdsc: Avoid actual power off until sync state
> >   clk: qcom: Add sync state callback to all providers
> >
> >  drivers/base/power/domain.c            | 18 ++++++++++--------
> >  drivers/clk/qcom/apss-ipq6018.c        |  1 +
> >  drivers/clk/qcom/camcc-sc7180.c        |  1 +
> >  drivers/clk/qcom/camcc-sc7280.c        |  1 +
> >  drivers/clk/qcom/camcc-sdm845.c        |  1 +
> >  drivers/clk/qcom/camcc-sm6350.c        |  1 +
> >  drivers/clk/qcom/camcc-sm8250.c        |  1 +
> >  drivers/clk/qcom/camcc-sm8450.c        |  1 +
> >  drivers/clk/qcom/common.c              | 19 +++++++++++++++++++
> >  drivers/clk/qcom/common.h              |  2 ++
> >  drivers/clk/qcom/dispcc-qcm2290.c      |  1 +
> >  drivers/clk/qcom/dispcc-sc7180.c       |  1 +
> >  drivers/clk/qcom/dispcc-sc7280.c       |  1 +
> >  drivers/clk/qcom/dispcc-sc8280xp.c     |  1 +
> >  drivers/clk/qcom/dispcc-sdm845.c       |  1 +
> >  drivers/clk/qcom/dispcc-sm6115.c       |  1 +
> >  drivers/clk/qcom/dispcc-sm6125.c       |  1 +
> >  drivers/clk/qcom/dispcc-sm6350.c       |  1 +
> >  drivers/clk/qcom/dispcc-sm6375.c       |  1 +
> >  drivers/clk/qcom/dispcc-sm8250.c       |  1 +
> >  drivers/clk/qcom/dispcc-sm8450.c       |  1 +
> >  drivers/clk/qcom/dispcc-sm8550.c       |  1 +
> >  drivers/clk/qcom/gcc-apq8084.c         |  1 +
> >  drivers/clk/qcom/gcc-ipq806x.c         |  1 +
> >  drivers/clk/qcom/gcc-ipq8074.c         |  1 +
> >  drivers/clk/qcom/gcc-mdm9615.c         |  1 +
> >  drivers/clk/qcom/gcc-msm8660.c         |  1 +
> >  drivers/clk/qcom/gcc-msm8909.c         |  1 +
> >  drivers/clk/qcom/gcc-msm8916.c         |  1 +
> >  drivers/clk/qcom/gcc-msm8939.c         |  1 +
> >  drivers/clk/qcom/gcc-msm8953.c         |  1 +
> >  drivers/clk/qcom/gcc-msm8960.c         |  1 +
> >  drivers/clk/qcom/gcc-msm8974.c         |  1 +
> >  drivers/clk/qcom/gcc-msm8976.c         |  1 +
> >  drivers/clk/qcom/gcc-msm8994.c         |  1 +
> >  drivers/clk/qcom/gcc-msm8996.c         |  1 +
> >  drivers/clk/qcom/gcc-msm8998.c         |  1 +
> >  drivers/clk/qcom/gcc-qcm2290.c         |  1 +
> >  drivers/clk/qcom/gcc-qcs404.c          |  1 +
> >  drivers/clk/qcom/gcc-qdu1000.c         |  1 +
> >  drivers/clk/qcom/gcc-sa8775p.c         |  1 +
> >  drivers/clk/qcom/gcc-sc7180.c          |  1 +
> >  drivers/clk/qcom/gcc-sc7280.c          |  1 +
> >  drivers/clk/qcom/gcc-sc8180x.c         |  1 +
> >  drivers/clk/qcom/gcc-sc8280xp.c        |  1 +
> >  drivers/clk/qcom/gcc-sdm660.c          |  1 +
> >  drivers/clk/qcom/gcc-sdm845.c          |  1 +
> >  drivers/clk/qcom/gcc-sdx55.c           |  1 +
> >  drivers/clk/qcom/gcc-sdx65.c           |  1 +
> >  drivers/clk/qcom/gcc-sm6115.c          |  1 +
> >  drivers/clk/qcom/gcc-sm6125.c          |  1 +
> >  drivers/clk/qcom/gcc-sm6350.c          |  1 +
> >  drivers/clk/qcom/gcc-sm6375.c          |  1 +
> >  drivers/clk/qcom/gcc-sm7150.c          |  1 +
> >  drivers/clk/qcom/gcc-sm8150.c          |  1 +
> >  drivers/clk/qcom/gcc-sm8250.c          |  1 +
> >  drivers/clk/qcom/gcc-sm8350.c          |  1 +
> >  drivers/clk/qcom/gcc-sm8450.c          |  1 +
> >  drivers/clk/qcom/gcc-sm8550.c          |  1 +
> >  drivers/clk/qcom/gdsc.c                | 26 ++++++++++++++++++++++++++
> >  drivers/clk/qcom/gdsc.h                |  6 ++++++
> >  drivers/clk/qcom/gpucc-msm8998.c       |  1 +
> >  drivers/clk/qcom/gpucc-sc7180.c        |  1 +
> >  drivers/clk/qcom/gpucc-sc7280.c        |  1 +
> >  drivers/clk/qcom/gpucc-sc8280xp.c      |  1 +
> >  drivers/clk/qcom/gpucc-sdm660.c        |  1 +
> >  drivers/clk/qcom/gpucc-sdm845.c        |  1 +
> >  drivers/clk/qcom/gpucc-sm6115.c        |  1 +
> >  drivers/clk/qcom/gpucc-sm6125.c        |  1 +
> >  drivers/clk/qcom/gpucc-sm6350.c        |  1 +
> >  drivers/clk/qcom/gpucc-sm6375.c        |  1 +
> >  drivers/clk/qcom/gpucc-sm8150.c        |  1 +
> >  drivers/clk/qcom/gpucc-sm8250.c        |  1 +
> >  drivers/clk/qcom/gpucc-sm8350.c        |  1 +
> >  drivers/clk/qcom/lcc-ipq806x.c         |  1 +
> >  drivers/clk/qcom/lpassaudiocc-sc7280.c |  1 +
> >  drivers/clk/qcom/lpasscc-sc7280.c      |  1 +
> >  drivers/clk/qcom/lpasscorecc-sc7180.c  |  2 ++
> >  drivers/clk/qcom/lpasscorecc-sc7280.c  |  2 ++
> >  drivers/clk/qcom/mmcc-apq8084.c        |  1 +
> >  drivers/clk/qcom/mmcc-msm8974.c        |  1 +
> >  drivers/clk/qcom/mmcc-msm8994.c        |  1 +
> >  drivers/clk/qcom/mmcc-msm8996.c        |  1 +
> >  drivers/clk/qcom/mmcc-msm8998.c        |  1 +
> >  drivers/clk/qcom/mmcc-sdm660.c         |  1 +
> >  drivers/clk/qcom/videocc-sc7180.c      |  1 +
> >  drivers/clk/qcom/videocc-sc7280.c      |  1 +
> >  drivers/clk/qcom/videocc-sdm845.c      |  1 +
> >  drivers/clk/qcom/videocc-sm8150.c      |  1 +
> >  drivers/clk/qcom/videocc-sm8250.c      |  1 +
> >  drivers/soc/qcom/rpmhpd.c              | 19 +++++++------------
> >  include/linux/pm_domain.h              |  4 ++++
> >  92 files changed, 161 insertions(+), 20 deletions(-)
> >
> > --
> > 2.34.1
> >