Message-ID: <20220219114520.GG31965@dragon>
Date:   Sat, 19 Feb 2022 19:45:21 +0800
From:   Shawn Guo <shawn.guo@...aro.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Maulik Shah <quic_mkshah@...cinc.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/3] cpuidle: psci: Call cpu_cluster_pm_enter() on the
 last CPU

On Thu, Feb 17, 2022 at 09:37:03PM +0800, Shawn Guo wrote:
> On Thu, Feb 17, 2022 at 08:52:35AM +0000, Marc Zyngier wrote:
> > On Thu, 17 Feb 2022 07:31:32 +0000,
> > Shawn Guo <shawn.guo@...aro.org> wrote:
> > > 
> > > On Wed, Feb 16, 2022 at 03:58:41PM +0000, Marc Zyngier wrote:
> > > > On 2022-02-16 14:49, Sudeep Holla wrote:
> > > > > +Ulf (as you he is the author of cpuidle-psci-domains.c and can help you
> > > > > with that if you require)
> > > 
> > > Thanks, Sudeep!
> > > 
> > > > > 
> > > > > On Wed, Feb 16, 2022 at 09:28:28PM +0800, Shawn Guo wrote:
> > > > > > Make a call to cpu_cluster_pm_enter() on the last CPU going to low
> > > > > > power
> > > > > > state (and cpu_cluster_pm_exit() on the firt CPU coming back), so that
> > > > > > platforms can be notified to set up hardware for getting into the
> > > > > > cluster
> > > > > > low power state.
> > > > > > 
> > > > > 
> > > > > NACK. We are not getting the notion of CPU cluster back to cpuidle
> > > > > again.
> > > > > That must die. Remember the cluster doesn't map to idle states
> > > > > especially
> > > > > in the DSU systems where HMP CPUs are in the same cluster but can be in
> > > > > different power domains.
> > > 
> > > The 'cluster' in cpu_cluster_pm_enter() doesn't necessarily means
> > > a physical CPU cluster.  I think the documentation of the function has a
> > > better description.
> > > 
> > >  * Notifies listeners that all cpus in a power domain are entering a low power
> > >  * state that may cause some blocks in the same power domain to reset.
> > > 
> > > So cpu_domain_pm_enter() might be a better name?  Anyways ...
> > > 
> > > > > 
> > > > > You need to decide which PSCI CPU_SUSPEND mode you want to use first. If
> > > > > it is
> > > > > Platform Co-ordinated(PC), then you need not notify anything to the
> > > > > platform.
> > > > > Just request the desired idle state on each CPU and platform will take
> > > > > care
> > > > > from there.
> > > > > 
> > > > > If for whatever reason you have chosen OS initiated mode(OSI), then
> > > > > specify
> > > > > the PSCI power domains correctly in the DT which will make use of the
> > > > > cpuidle-psci-domains and handle the so called "cluster" state correctly.
> > > 
> > > Yes, I'm running a Qualcomm platform that has OSI supported in PSCI.
> > > 
> > > > 
> > > > My understanding is that what Shawn is after is a way to detect the "last
> > > > man standing" on the system to kick off some funky wake-up controller that
> > > > really should be handled by the power controller (because only that guy
> > > > knows for sure who is the last CPU on the block).
> > > > 
> > > > There was previously some really funky stuff (copy pasted from the existing
> > > > rpmh_rsc_cpu_pm_callback()), which I totally objected to having hidden in
> > > > an irqchip driver.
> > > > 
> > > > My ask was that if we needed such information, and assuming that it is
> > > > possible to obtain it in a reliable way, this should come from the core
> > > > code, and not be invented by random drivers.
> > > 
> > > Thanks Marc for explain my problem!
> > > 
> > > Right, all I need is a notification in MPM irqchip driver when the CPU
> > > domain/cluster is about to enter low power state.  As cpu_pm -
> > > kernel/cpu_pm.c, already has helper cpu_cluster_pm_enter() sending
> > > CPU_CLUSTER_PM_ENTER event, I just need to find a caller to this cpu_pm
> > > helper.  
> > > 
> > > Is .power_off hook of generic_pm_domain a better place for calling the
> > > helper?
> > 
> > I really don't understand why you want a cluster PM event generated by
> > the idle driver.  Specially considering that you are not after a
> > *cluster* PM event, but after some sort of system-wide event (last man
> > standing).
> 
> That's primarily because MPM driver is used in the idle context, either
> s2idle or cpuidle, and idle driver already has some infrastructure that
> could help trigger the event.
> 
> > It looks to me that having a predicate that can be called from a PM
> > notifier event to find out whether you're the last in line would be
> > better suited, and could further be used to remove the crap from the
> > rpmh-rsc driver.
> 
> I will see if I can come up with a patch for discussion.

How about this?

---8<-----------
>From 0176b2311764959bb5f3322865bf85440eaf769e Mon Sep 17 00:00:00 2001
From: Shawn Guo <shawn.guo@...aro.org>
Date: Sat, 19 Feb 2022 13:35:47 +0800
Subject: [PATCH] PM: cpu: Add CPU_LAST_PM_ENTER and CPU_FIRST_PM_EXIT support

It becomes a common situation on some platforms that certain hardware
setup needs to be done on the last standing cpu, and rpmh-rsc[1] is such
an existing example.  As figuring out the last standing cpu is really
something generic, it adds CPU_LAST_PM_ENTER (and CPU_FIRST_PM_EXIT)
event support to cpu_pm helper, so that individual driver can be
notified when the last standing cpu is about to enter low power state.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/soc/qcom/rpmh-rsc.c?id=v5.16#n773

Signed-off-by: Shawn Guo <shawn.guo@...aro.org>
---
 include/linux/cpu_pm.h | 15 +++++++++++++++
 kernel/cpu_pm.c        | 33 +++++++++++++++++++++++++++++++--
 2 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/include/linux/cpu_pm.h b/include/linux/cpu_pm.h
index 552b8f9ea05e..153344307b7c 100644
--- a/include/linux/cpu_pm.h
+++ b/include/linux/cpu_pm.h
@@ -55,6 +55,21 @@ enum cpu_pm_event {
 
 	/* A cpu power domain is exiting a low power state */
 	CPU_CLUSTER_PM_EXIT,
+
+	/*
+	 * A cpu is entering a low power state after all other cpus
+	 * in the system have entered the lower power state.
+	 */
+	CPU_LAST_PM_ENTER,
+
+	/* The last cpu failed to enter a low power state */
+	CPU_LAST_PM_ENTER_FAILED,
+
+	/*
+	 * A cpu is exiting a low power state before any other cpus
+	 * in the system exits the low power state.
+	 */
+	CPU_FIRST_PM_EXIT,
 };
 
 #ifdef CONFIG_CPU_PM
diff --git a/kernel/cpu_pm.c b/kernel/cpu_pm.c
index 246efc74e3f3..7c104446e1e9 100644
--- a/kernel/cpu_pm.c
+++ b/kernel/cpu_pm.c
@@ -26,6 +26,8 @@ static struct {
 	.lock  = __RAW_SPIN_LOCK_UNLOCKED(cpu_pm_notifier.lock),
 };
 
+static atomic_t cpus_in_pm;
+
 static int cpu_pm_notify(enum cpu_pm_event event)
 {
 	int ret;
@@ -116,7 +118,20 @@ EXPORT_SYMBOL_GPL(cpu_pm_unregister_notifier);
  */
 int cpu_pm_enter(void)
 {
-	return cpu_pm_notify_robust(CPU_PM_ENTER, CPU_PM_ENTER_FAILED);
+	int ret;
+
+	ret = cpu_pm_notify_robust(CPU_PM_ENTER, CPU_PM_ENTER_FAILED);
+	if (ret)
+		return ret;
+
+	if (atomic_inc_return(&cpus_in_pm) == num_online_cpus()) {
+		ret = cpu_pm_notify_robust(CPU_LAST_PM_ENTER,
+					   CPU_LAST_PM_ENTER_FAILED);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(cpu_pm_enter);
 
@@ -134,7 +149,21 @@ EXPORT_SYMBOL_GPL(cpu_pm_enter);
  */
 int cpu_pm_exit(void)
 {
-	return cpu_pm_notify(CPU_PM_EXIT);
+	int ret;
+
+	ret = cpu_pm_notify(CPU_PM_EXIT);
+	if (ret)
+		return ret;
+
+	if (atomic_read(&cpus_in_pm) == num_online_cpus()) {
+		ret = cpu_pm_notify(CPU_FIRST_PM_EXIT);
+		if (ret)
+			return ret;
+	}
+
+	atomic_dec(&cpus_in_pm);
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(cpu_pm_exit);
 
-- 
2.17.1

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