From: Sudeep Holla <sudeep.holla@arm.com>
To: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Maulik Shah <mkshah@codeaurora.org>,
swboyd@chromium.org, agross@kernel.org, david.brown@linaro.org,
Lorenzo.Pieralisi@arm.com, linux-arm-msm@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, evgreen@chromium.org,
dianders@chromium.org, rnayak@codeaurora.org,
ilina@codeaurora.org, lsrao@codeaurora.org,
ulf.hansson@linaro.org, rjw@rjwysocki.net
Subject: Re: [PATCH v3 5/7] drivers: firmware: psci: Add hierarchical domain idle states converter
Date: Fri, 7 Feb 2020 11:25:09 +0000 [thread overview]
Message-ID: <20200207112508.GB40103@bogus> (raw)
In-Reply-To: <20200206211133.GR2514@yoga>
On Thu, Feb 06, 2020 at 01:11:33PM -0800, Bjorn Andersson wrote:
> On Wed 05 Feb 06:06 PST 2020, Sudeep Holla wrote:
>
> > On Wed, Feb 05, 2020 at 05:53:00PM +0530, Maulik Shah wrote:
> > >
> > > On 2/4/2020 8:51 PM, Sudeep Holla wrote:
> > > > 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@linaro.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 ?
> > >
> > > Hi Sudeep,
> > >
> > > there are cases like,
> > >
> > > Last cpu going to deepest idle mode need to lower various resoruce
> > > requirements (for eg DDR freq).
> > >
> >
> > In PC mode, only PSCI implementation knows the last man and there shouldn't
> > be any notion of it in OS. If you need it, you may need OSI. You are still
> > mixing up the things. NACK for any such approach, sorry.
> >
>
> Forgive me if I'm misunderstanding PSCI's role here, but doesn't it deal
> with the power management of the "processor subsystem" in the SoC?
>
Yes.
> In the Qualcomm platforms most resources (voltage rails, clocks, etc)
> are controlled through a power controller that provides controls for a
> state when the CPU subsystem is running and when it's asleep. This
> allows non-CPU-related device to control if resources that are shared
> with the CPU subsystem should be kept on when the last CPU/cluster goes
> down.
>
I understand that.
> An example of this would be the display controller voting to keep a
> voltage rail on after the CPU subsystem collapses, because the display
> is still on.
>
OK
> But as long as the CPU subsystem is running it will keep these resources
> available and there's no need to change these votes (e.g. if the display
> is turned on and off while the CPU is active the sleep-requests cancels
> out), so they are simply cached/batched up in the RPMh driver and what
> Maulik's series is attempting to do is to flush the cached values when
> Linux believes that the firmware might decide to enter a lower power
> state.
>
I understand all these. What I am arguing is that in PC mode, PSCI
firmware is the one who needs to vote and not OSPM because it is
responsible for pulling the plugs off the CPU/Cluster. So lets us not
bring that to OSPM. OSI was invented to do all such crazy things in OSPM,
please feel free to play with that ;-)
--
Regards,
Sudeep
next prev parent reply other threads:[~2020-02-07 11:25 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-03 13:35 [PATCH v3 0/7] Add RSC power domain support Maulik Shah
2020-02-03 13:35 ` [PATCH v3 1/7] drivers: qcom: rpmh: fix macro to accept NULL argument Maulik Shah
2020-02-03 13:35 ` [PATCH v3 2/7] drivers: qcom: rpmh: remove rpmh_flush export Maulik Shah
2020-02-03 13:35 ` [PATCH v3 3/7] dt-bindings: soc: qcom: Add RSC power domain specifier Maulik Shah
2020-02-03 13:35 ` [PATCH v3 4/7] drivers: qcom: rpmh-rsc: Add RSC power domain support Maulik Shah
2020-02-03 13:35 ` [PATCH v3 5/7] drivers: firmware: psci: Add hierarchical domain idle states converter Maulik Shah
2020-02-03 17:08 ` Sudeep Holla
2020-02-04 4:52 ` Maulik Shah
2020-02-04 15:21 ` Sudeep Holla
2020-02-05 12:23 ` Maulik Shah
2020-02-05 14:06 ` Sudeep Holla
2020-02-05 15:55 ` Ulf Hansson
2020-02-05 16:18 ` Sudeep Holla
2020-02-06 8:45 ` Ulf Hansson
2020-02-06 20:45 ` Lina Iyer
2020-02-07 11:20 ` Sudeep Holla
2020-02-07 12:32 ` Ulf Hansson
2020-02-07 14:48 ` Lorenzo Pieralisi
2020-02-07 15:52 ` Ulf Hansson
2020-02-07 16:15 ` Sudeep Holla
2020-02-08 10:25 ` Ulf Hansson
2020-02-10 10:31 ` Sudeep Holla
2020-02-07 16:05 ` Sudeep Holla
2020-02-06 21:11 ` Bjorn Andersson
2020-02-07 11:25 ` Sudeep Holla [this message]
2020-02-03 13:35 ` [PATCH v3 6/7] arm64: dts: qcom: sc7180: Add cpuidle low power states Maulik Shah
2020-02-04 23:15 ` Matthias Kaehlcke
2020-02-05 12:07 ` Maulik Shah
2020-02-03 13:35 ` [PATCH v3 7/7] arm64: dts: qcom: sc7180: Convert to the hierarchical CPU topology layout Maulik Shah
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