linux-kernel - Re: [PATCH v3 5/7] drivers: firmware: psci: Add hierarchical domain idle states converter

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Date:   Tue, 4 Feb 2020 15:21:32 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Maulik Shah <mkshah@...eaurora.org>
Cc:     swboyd@...omium.org, agross@...nel.org, david.brown@...aro.org,
        Lorenzo.Pieralisi@....com, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, bjorn.andersson@...aro.org,
        evgreen@...omium.org, dianders@...omium.org, rnayak@...eaurora.org,
        ilina@...eaurora.org, lsrao@...eaurora.org, ulf.hansson@...aro.org,
        rjw@...ysocki.net, Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH v3 5/7] drivers: firmware: psci: Add hierarchical domain
 idle states converter

On Tue, Feb 04, 2020 at 10:22:42AM +0530, Maulik Shah wrote:
>
> On 2/3/2020 10:38 PM, Sudeep Holla wrote:
> > On Mon, Feb 03, 2020 at 07:05:38PM +0530, Maulik Shah wrote:
> > > From: Ulf Hansson <ulf.hansson@...aro.org>
> > >
> > > If the hierarchical CPU topology is used, but the OS initiated mode isn't
> > > supported, we need to rely solely on the regular cpuidle framework to
> > > manage the idle state selection, rather than using genpd and its
> > > governor.
> > >
> > > For this reason, introduce a new PSCI DT helper function,
> > > psci_dt_pm_domains_parse_states(), which parses and converts the
> > > hierarchically described domain idle states from DT, into regular flattened
> > > cpuidle states. The converted states are added to the existing cpuidle
> > > driver's array of idle states, which make them available for cpuidle.
> > >
> > And what's the main motivation for this if OSI is not supported in the
> > firmware ?
>
> Hi Sudeep,
>
> Main motivation is to do last-man activities before the CPU cluster can
> enter a deep idle state.
>

Details on those last-man activities will help the discussion. Basically
I am wondering what they are and why they need to done in OSPM ?

> > > Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> > > [applied to new path, resolved conflicts]
> > > Signed-off-by: Maulik Shah <mkshah@...eaurora.org>
> > > ---
> > >   drivers/cpuidle/cpuidle-psci-domain.c | 137 +++++++++++++++++++++++++++++-----
> > >   drivers/cpuidle/cpuidle-psci.c        |  41 +++++-----
> > >   drivers/cpuidle/cpuidle-psci.h        |  11 +++
> > >   3 files changed, 153 insertions(+), 36 deletions(-)
> > >
> > > diff --git a/drivers/cpuidle/cpuidle-psci-domain.c b/drivers/cpuidle/cpuidle-psci-domain.c
> > > index 423f03b..3c417f7 100644
> > > --- a/drivers/cpuidle/cpuidle-psci-domain.c
> > > +++ b/drivers/cpuidle/cpuidle-psci-domain.c
> > > @@ -26,13 +26,17 @@ struct psci_pd_provider {
> > >   };
> > >
> > >   static LIST_HEAD(psci_pd_providers);
> > > -static bool osi_mode_enabled __initdata;
> > > +static bool osi_mode_enabled;
> > >
> > >   static int psci_pd_power_off(struct generic_pm_domain *pd)
> > >   {
> > >   	struct genpd_power_state *state = &pd->states[pd->state_idx];
> > >   	u32 *pd_state;
> > >
> > > +	/* If we have failed to enable OSI mode, then abort power off. */
> > > +	if ((psci_has_osi_support()) && !osi_mode_enabled)
> > > +		return -EBUSY;
> > > +
> > Why is this needed ? IIUC we don't create genpd domains if OSI is not
> > enabled.
>
> we do create genpd domains, for cpu domains, we just abort power off here
> since idle states are converted into regular flattened mode.
>

OK, IIRC the OSI patches from Ulf didn't add the genpd or rather removed
them in case of any failure to enable OSI. Has that been changed ? If so,
why ?

> however genpd poweroff will be used by parent domain (rsc in this case)
> which is kept in hireachy in DTSI with cluster domain to do last man
> activities.
>

I am bit confused here. Either we do OSI or PC and what you are describing
sounds like a mix-n-match to me and I am totally against it.

--
Regards,
Sudeep