Message-ID: <1ca666c336ebee569a429e729d5ae547@codeaurora.org>
Date:   Thu, 13 Aug 2020 22:56:20 +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>
Subject: Re: [PATCH 1/2] PM / Domains: Add GENPD_FLAG_SUSPEND_ON flag

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.

> 
> Then in the suspend_noirq phase, genpd tries to power off the PM
> domain, unless there are wakeups to consider.
> 
> Taking the above into account, wouldn't that mean that you potentially
> may end up keeping the PM domain powered on, even if it actually can
> be powered off in the suspend_noirq phase by genpd?
> 
> Kind regards
> Uffe
> 
>> >
>> >>
>> >> Signed-off-by: Sibi Sankar <sibis@...eaurora.org>
>> >> ---
>> >>  drivers/base/power/domain.c | 3 ++-
>> >>  include/linux/pm_domain.h   | 5 +++++
>> >>  2 files changed, 7 insertions(+), 1 deletion(-)
>> >>
>> >> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
>> >> index 2cb5e04cf86cd..ba78ac4a450d4 100644
>> >> --- a/drivers/base/power/domain.c
>> >> +++ b/drivers/base/power/domain.c
>> >> @@ -129,6 +129,7 @@ static const struct genpd_lock_ops genpd_spin_ops
>> >> = {
>> >>  #define genpd_is_active_wakeup(genpd)  (genpd->flags &
>> >> GENPD_FLAG_ACTIVE_WAKEUP)
>> >>  #define genpd_is_cpu_domain(genpd)     (genpd->flags &
>> >> GENPD_FLAG_CPU_DOMAIN)
>> >>  #define genpd_is_rpm_always_on(genpd)  (genpd->flags &
>> >> GENPD_FLAG_RPM_ALWAYS_ON)
>> >> +#define genpd_is_suspend_on(genpd)     (genpd->flags &
>> >> GENPD_FLAG_SUSPEND_ON)
>> >>
>> >>  static inline bool irq_safe_dev_in_no_sleep_domain(struct device
>> >> *dev,
>> >>                 const struct generic_pm_domain *genpd)
>> >> @@ -949,7 +950,7 @@ static void genpd_sync_power_off(struct
>> >> generic_pm_domain *genpd, bool use_lock,
>> >>  {
>> >>         struct gpd_link *link;
>> >>
>> >> -       if (!genpd_status_on(genpd) || genpd_is_always_on(genpd))
>> >> +       if (!genpd_status_on(genpd) || genpd_is_always_on(genpd) ||
>> >> genpd_is_suspend_on(genpd))
>> >>                 return;
>> >>
>> >>         if (genpd->suspended_count != genpd->device_count
>> >> diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
>> >> index ee11502a575b0..3002a2d68936a 100644
>> >> --- a/include/linux/pm_domain.h
>> >> +++ b/include/linux/pm_domain.h
>> >> @@ -55,6 +55,10 @@
>> >>   *
>> >>   * GENPD_FLAG_RPM_ALWAYS_ON:   Instructs genpd to always keep the PM
>> >> domain
>> >>   *                             powered on except for system suspend.
>> >> + *
>> >> + * GENPD_FLAG_SUSPEND_ON:      Instructs genpd to keep the PM domain
>> >> powered
>> >> + *                             on during suspend and runtime PM
>> >> controlled
>> >> + *                             otherwise.
>> >>   */
>> >>  #define GENPD_FLAG_PM_CLK       (1U << 0)
>> >>  #define GENPD_FLAG_IRQ_SAFE     (1U << 1)
>> >> @@ -62,6 +66,7 @@
>> >>  #define GENPD_FLAG_ACTIVE_WAKEUP (1U << 3)
>> >>  #define GENPD_FLAG_CPU_DOMAIN   (1U << 4)
>> >>  #define GENPD_FLAG_RPM_ALWAYS_ON (1U << 5)
>> >> +#define GENPD_FLAG_SUSPEND_ON   (1U << 6)
>> >>
>> >>  enum gpd_status {
>> >>         GPD_STATE_ACTIVE = 0,   /* PM domain is active */
>> >> --
>> >> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
>> >> Forum,
>> >> a Linux Foundation Collaborative Project
>> >>
>> 
>> --
>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
>> a Linux Foundation Collaborative Project.

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project.

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