linux-kernel - Re: [PATCH 1/2] PM / Domains: Add GENPD_FLAG_SUSPEND

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Message-ID: <de2cde2767d303a1334c7aa71d178aa2@codeaurora.org>
Date:   Tue, 18 Aug 2020 14:33:20 +0530
From:   Sibi Sankar <sibis@...eaurora.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Andy Gross <agross@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Doug Anderson <dianders@...omium.org>,
        linux-kernel-owner@...r.kernel.org,
        Kevin Hilman <khilman@...nel.org>,
        linux-arm-msm-owner@...r.kernel.org
Subject: Re: [PATCH 1/2] PM / Domains: Add GENPD_FLAG_SUSPEND_ON flag

On 2020-08-18 14:01, Ulf Hansson wrote:
> On Mon, 17 Aug 2020 at 18:49, Sibi Sankar <sibis@...eaurora.org> wrote:
>> 
>> On 2020-08-17 14:14, Ulf Hansson wrote:
>> > On Thu, 13 Aug 2020 at 19:26, Sibi Sankar <sibis@...eaurora.org> wrote:
>> >>
>> >> On 2020-08-13 18:04, Ulf Hansson wrote:
>> >> > On Wed, 12 Aug 2020 at 19:03, Sibi Sankar <sibis@...eaurora.org> wrote:
>> >> >>
>> >> >> Uffe,
>> >> >> Thanks for taking time to review the
>> >> >> series!
>> >> >>
>> >> >> On 2020-08-12 15:15, Ulf Hansson wrote:
>> >> >> > On Tue, 11 Aug 2020 at 21:03, Sibi Sankar <sibis@...eaurora.org> wrote:
>> >> >> >>
>> >> >> >> This is for power domains which needs to stay powered on for suspend
>> >> >> >> but can be powered on/off as part of runtime PM. This flag is aimed at
>> >> >> >> power domains coupled to remote processors which enter suspend states
>> >> >> >> independent to that of the application processor. Such power domains
>> >> >> >> are turned off only on remote processor crash/shutdown.
>> >> >> >
>> >> >> > As Kevin also requested, please elaborate more on the use case.
>> >> >> >
>> >> >> > Why exactly must the PM domain stay powered on during system suspend?
>> >> >> > Is there a wakeup configured that needs to be managed - or is there a
>> >> >> > co-processor/FW behaviour that needs to be obeyed to?
>> >> >>
>> >> >> Yes this is a co-processor behavior that
>> >> >> needs to be obeyed. Specifically application
>> >> >> processor notifies the Always on Subsystem
>> >> >> (AOSS) that a particular co-processor is up
>> >> >> using the power domains exposed by AOSS QMP
>> >> >> driver. AOSS uses this information to wait
>> >> >> for the co-processors to suspend before
>> >> >> starting its sleep sequence. The application
>> >> >> processor powers off these power domains only
>> >> >> if the co-processor has crashed or powered
>> >> >> off.
>> >> >
>> >> > Thanks for clarifying!
>> >> >
>> >> > Although, can you please elaborate a bit more on the actual use case?
>> >> > What are the typical co-processor and what drivers are involved in
>> >> > managing it?
>> >>
>> >> The co-processors using the power domains
>> >> exposed by qcom_aoss driver are modem,
>> >> audio dsp, compute dsp managed using
>> >> qcom_q6v5_mss and qcom_q6v5_pas driver.
>> >>
>> >> >
>> >> > As you may know, runtime PM becomes disabled during system suspend of
>> >> > a device. Which means, if the driver tries to power off the
>> >> > coprocessor (via calling pm_runtime_put() for example), somewhere in
>> >> > the system suspend phase of the corresponding device, its attached PM
>> >> > domain stays powered on when managed by genpd.
>> >>
>> >> The drivers aren't really expected
>> >> do anything during suspend/resume
>> >> pretty much because the co-processors
>> >> enter low-power modes independent to
>> >> that of the application processor. On
>> >> co-processor crash the remoteproc core
>> >> does a pm_stay_awake followed by a
>> >> pm_relax after crash recovery.
>> >
>> > Okay, thanks again for clarifying. You have convinced me about the
>> > need for a new flag to cope with these use cases.
>> >
>> > Would you mind updating the commit message with some of the
>> > information you just provided?
>> >
>> > Additionally, to make it clear that the flag should be used to keep
>> > the PM domain powered on during system suspend, but only if it's
>> > already powered on - please rename the flag to GENPD_FLAG_NO_SUSPEND,
>> > and update the corresponding description of it in the header file.
>> 
>> Thanks, naming it ^^ makes more sense :)
>> 
>> https://lore.kernel.org/lkml/340a7aafcf0301ff3158a4e211992041@codeaurora.org/
>> 
>> Also we wouldn't want to power on
>> runtime suspended power domains with
>> the NO_SUSPEND flag set, on resume as
>> explained ^^. Do you agree with that
>> as well?
> 
> Actually no.
> 
> Instead, I think that deserves a separate flag, as it may very well
> turn out that resuming can be skipped for other cases than
> "NO_SUSPEND".
> 
> Therefore, please add a GENPD_FLAG_NO_RESUME for this.

Thanks I'll do that in v2

> 
> Kind regards
> Uffe

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