[PATCH 0/6] pmdomain/cpuidle-psci: Support s2idle/s2ram on PREEMPT_RT

[PATCH 0/6] pmdomain/cpuidle-psci: Support s2idle/s2ram on PREEMPT_RT

[Ulf Hansson]

The hierarchical PM domain topology and the corresponding domain-idle-states
are currently disabled on a PREEMPT_RT based configuration. The main reason is
because spinlocks are turned into sleepable locks on PREEMPT_RT, which means
genpd and runtime PM can't be use in the atomic idle-path when
selecting/entering an idle-state.

For s2idle/s2ram this is an unnecessary limitation that this series intends to
address. Note that, the support for cpuhotplug is left to future improvements.
More information about this are available in the commit messages.

I have tested this on a Dragonboard 410c.

Kind regards
Ulf Hansson


Ulf Hansson (6):
  pmdomain: core: Enable s2idle for CPU PM domains on PREEMPT_RT
  pmdomain: core: Don't hold the genpd-lock when calling
    dev_pm_domain_set()
  cpuidle: psci-domain: Enable system-wide suspend on PREEMPT_RT
  cpuidle: psci: Drop redundant assignment of CPUIDLE_FLAG_RCU_IDLE
  cpuidle: psci: Enable the hierarchical topology for s2ram on
    PREEMPT_RT
  cpuidle: psci: Enable the hierarchical topology for s2idle on
    PREEMPT_RT

 drivers/cpuidle/cpuidle-psci-domain.c | 10 ++++--
 drivers/cpuidle/cpuidle-psci.c        | 26 +++++++++-----
 drivers/pmdomain/core.c               | 52 +++++++++++++++++++++++++--
 include/linux/pm_domain.h             |  5 ++-
 4 files changed, 77 insertions(+), 16 deletions(-)

-- 
2.34.1


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH 1/6] pmdomain: core: Enable s2idle for CPU PM domains on PREEMPT_RT

[Ulf Hansson]

To allow a genpd provider for a CPU PM domain to enter a domain-idle-state
during s2idle on a PREEMPT_RT based configuration, we can't use the regular
spinlock, as they are turned into sleepable locks on PREEMPT_RT.

To address this problem, let's convert into using the raw spinlock, but
only for genpd providers that have the GENPD_FLAG_CPU_DOMAIN bit set. In
this way, the lock can still be acquired/released in atomic context, which
is needed in the idle-path for PREEMPT_RT.

Do note that the genpd power-on/off notifiers may also be fired during
s2idle, but these are already prepared for PREEMPT_RT as they are based on
the raw notifiers. However, consumers of them may need to adopt accordingly
to work properly on PREEMPT_RT.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
---
 drivers/pmdomain/core.c   | 47 ++++++++++++++++++++++++++++++++++++++-
 include/linux/pm_domain.h |  5 ++++-
 2 files changed, 50 insertions(+), 2 deletions(-)

diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
index 342779464c0d..abd3c069df8b 100644
--- a/drivers/pmdomain/core.c
+++ b/drivers/pmdomain/core.c
@@ -117,6 +117,48 @@ static const struct genpd_lock_ops genpd_spin_ops = {
 	.unlock = genpd_unlock_spin,
 };
 
+static void genpd_lock_raw_spin(struct generic_pm_domain *genpd)
+	__acquires(&genpd->raw_slock)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&genpd->raw_slock, flags);
+	genpd->raw_lock_flags = flags;
+}
+
+static void genpd_lock_nested_raw_spin(struct generic_pm_domain *genpd,
+					int depth)
+	__acquires(&genpd->raw_slock)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave_nested(&genpd->raw_slock, flags, depth);
+	genpd->raw_lock_flags = flags;
+}
+
+static int genpd_lock_interruptible_raw_spin(struct generic_pm_domain *genpd)
+	__acquires(&genpd->raw_slock)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&genpd->raw_slock, flags);
+	genpd->raw_lock_flags = flags;
+	return 0;
+}
+
+static void genpd_unlock_raw_spin(struct generic_pm_domain *genpd)
+	__releases(&genpd->raw_slock)
+{
+	raw_spin_unlock_irqrestore(&genpd->raw_slock, genpd->raw_lock_flags);
+}
+
+static const struct genpd_lock_ops genpd_raw_spin_ops = {
+	.lock = genpd_lock_raw_spin,
+	.lock_nested = genpd_lock_nested_raw_spin,
+	.lock_interruptible = genpd_lock_interruptible_raw_spin,
+	.unlock = genpd_unlock_raw_spin,
+};
+
 #define genpd_lock(p)			p->lock_ops->lock(p)
 #define genpd_lock_nested(p, d)		p->lock_ops->lock_nested(p, d)
 #define genpd_lock_interruptible(p)	p->lock_ops->lock_interruptible(p)
@@ -2069,7 +2111,10 @@ static void genpd_free_data(struct generic_pm_domain *genpd)
 
 static void genpd_lock_init(struct generic_pm_domain *genpd)
 {
-	if (genpd->flags & GENPD_FLAG_IRQ_SAFE) {
+	if (genpd->flags & GENPD_FLAG_CPU_DOMAIN) {
+		raw_spin_lock_init(&genpd->raw_slock);
+		genpd->lock_ops = &genpd_raw_spin_ops;
+	} else if (genpd->flags & GENPD_FLAG_IRQ_SAFE) {
 		spin_lock_init(&genpd->slock);
 		genpd->lock_ops = &genpd_spin_ops;
 	} else {
diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
index 772d3280d35f..670392ecd076 100644
--- a/include/linux/pm_domain.h
+++ b/include/linux/pm_domain.h
@@ -194,8 +194,11 @@ struct generic_pm_domain {
 			spinlock_t slock;
 			unsigned long lock_flags;
 		};
+		struct {
+			raw_spinlock_t raw_slock;
+			unsigned long raw_lock_flags;
+		};
 	};
-
 };
 
 static inline struct generic_pm_domain *pd_to_genpd(struct dev_pm_domain *pd)
-- 
2.34.1


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH 2/6] pmdomain: core: Don't hold the genpd-lock when calling dev_pm_domain_set()

[Ulf Hansson]

There is no need to hold the genpd-lock, while assigning the
dev->pm_domain. In fact, it becomes a problem on a PREEMPT_RT based
configuration as the genpd-lock may be a raw spinlock, while the lock
acquired through the call to dev_pm_domain_set() is a regular spinlock.

To fix the problem, let's simply move the calls to dev_pm_domain_set()
outside the genpd-lock.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
---
 drivers/pmdomain/core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
index abd3c069df8b..1e3f8dea4654 100644
--- a/drivers/pmdomain/core.c
+++ b/drivers/pmdomain/core.c
@@ -1726,7 +1726,6 @@ static int genpd_add_device(struct generic_pm_domain *genpd, struct device *dev,
 	genpd_lock(genpd);
 
 	genpd_set_cpumask(genpd, gpd_data->cpu);
-	dev_pm_domain_set(dev, &genpd->domain);
 
 	genpd->device_count++;
 	if (gd)
@@ -1735,6 +1734,7 @@ static int genpd_add_device(struct generic_pm_domain *genpd, struct device *dev,
 	list_add_tail(&gpd_data->base.list_node, &genpd->dev_list);
 
 	genpd_unlock(genpd);
+	dev_pm_domain_set(dev, &genpd->domain);
  out:
 	if (ret)
 		genpd_free_dev_data(dev, gpd_data);
@@ -1791,12 +1791,13 @@ static int genpd_remove_device(struct generic_pm_domain *genpd,
 		genpd->gd->max_off_time_changed = true;
 
 	genpd_clear_cpumask(genpd, gpd_data->cpu);
-	dev_pm_domain_set(dev, NULL);
 
 	list_del_init(&pdd->list_node);
 
 	genpd_unlock(genpd);
 
+	dev_pm_domain_set(dev, NULL);
+
 	if (genpd->detach_dev)
 		genpd->detach_dev(genpd, dev);
 
-- 
2.34.1


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH 3/6] cpuidle: psci-domain: Enable system-wide suspend on PREEMPT_RT

[Ulf Hansson]

The domain-idle-states are currently disabled on a PREEMPT_RT based
configuration for the cpuidle-psci-domain. To enable them to be used for
system-wide suspend and in particular during s2idle, let's set the
GENPD_FLAG_RPM_ALWAYS_ON instead of GENPD_FLAG_ALWAYS_ON for the
corresponding genpd provider.

In this way, the runtime PM path remains disabled in genpd for its attached
devices, while powering-on/off the PM domain during system-wide suspend
becomes allowed.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
---
 drivers/cpuidle/cpuidle-psci-domain.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/cpuidle/cpuidle-psci-domain.c b/drivers/cpuidle/cpuidle-psci-domain.c
index fae958794339..ea28b73ef3fb 100644
--- a/drivers/cpuidle/cpuidle-psci-domain.c
+++ b/drivers/cpuidle/cpuidle-psci-domain.c
@@ -67,12 +67,16 @@ static int psci_pd_init(struct device_node *np, bool use_osi)
 
 	/*
 	 * Allow power off when OSI has been successfully enabled.
-	 * PREEMPT_RT is not yet ready to enter domain idle states.
+	 * On a PREEMPT_RT based configuration the domain idle states are
+	 * supported, but only during system-wide suspend.
 	 */
-	if (use_osi && !IS_ENABLED(CONFIG_PREEMPT_RT))
+	if (use_osi) {
 		pd->power_off = psci_pd_power_off;
-	else
+		if (IS_ENABLED(CONFIG_PREEMPT_RT))
+			pd->flags |= GENPD_FLAG_RPM_ALWAYS_ON;
+	} else {
 		pd->flags |= GENPD_FLAG_ALWAYS_ON;
+	}
 
 	/* Use governor for CPU PM domains if it has some states to manage. */
 	pd_gov = pd->states ? &pm_domain_cpu_gov : NULL;
-- 
2.34.1


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH 4/6] cpuidle: psci: Drop redundant assignment of CPUIDLE_FLAG_RCU_IDLE

[Ulf Hansson]

When using the hierarchical topology and PSCI OSI-mode we may end up
overriding the deepest idle-state's ->enter|enter_s2idle() callbacks, but
there is no point to also re-assign the CPUIDLE_FLAG_RCU_IDLE for the
idle-state in question, as that has already been set when parsing the
states from DT. See init_state_node().

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
---
 drivers/cpuidle/cpuidle-psci.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
index 782030a27703..d82a8bc1b194 100644
--- a/drivers/cpuidle/cpuidle-psci.c
+++ b/drivers/cpuidle/cpuidle-psci.c
@@ -234,7 +234,6 @@ static int psci_dt_cpu_init_topology(struct cpuidle_driver *drv,
 	 * of a shared state for the domain, assumes the domain states are all
 	 * deeper states.
 	 */
-	drv->states[state_count - 1].flags |= CPUIDLE_FLAG_RCU_IDLE;
 	drv->states[state_count - 1].enter = psci_enter_domain_idle_state;
 	drv->states[state_count - 1].enter_s2idle = psci_enter_s2idle_domain_idle_state;
 	psci_cpuidle_use_cpuhp = true;
-- 
2.34.1


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH 5/6] cpuidle: psci: Enable the hierarchical topology for s2ram on PREEMPT_RT

[Ulf Hansson]

The hierarchical PM domain topology are currently disabled on a PREEMPT_RT
based configuration. As a first step to enable it to be used, let's try to
attach the CPU devices to their PM domains on PREEMPT_RT. In this way the
syscore ops becomes available, allowing the PM domain topology to be
managed during s2ram.

For the moment let's leave the support for CPU hotplug outside PREEMPT_RT,
as it's depending on using runtime PM. For s2ram, this isn't a problem as
all CPUs are managed via the syscore ops.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
---
 drivers/cpuidle/cpuidle-psci.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
index d82a8bc1b194..ad6ce9fe12b4 100644
--- a/drivers/cpuidle/cpuidle-psci.c
+++ b/drivers/cpuidle/cpuidle-psci.c
@@ -37,6 +37,7 @@ struct psci_cpuidle_data {
 
 static DEFINE_PER_CPU_READ_MOSTLY(struct psci_cpuidle_data, psci_cpuidle_data);
 static DEFINE_PER_CPU(u32, domain_state);
+static bool psci_cpuidle_use_syscore;
 static bool psci_cpuidle_use_cpuhp;
 
 void psci_set_domain_state(u32 state)
@@ -166,6 +167,12 @@ static struct syscore_ops psci_idle_syscore_ops = {
 	.resume = psci_idle_syscore_resume,
 };
 
+static void psci_idle_init_syscore(void)
+{
+	if (psci_cpuidle_use_syscore)
+		register_syscore_ops(&psci_idle_syscore_ops);
+}
+
 static void psci_idle_init_cpuhp(void)
 {
 	int err;
@@ -173,8 +180,6 @@ static void psci_idle_init_cpuhp(void)
 	if (!psci_cpuidle_use_cpuhp)
 		return;
 
-	register_syscore_ops(&psci_idle_syscore_ops);
-
 	err = cpuhp_setup_state_nocalls(CPUHP_AP_CPU_PM_STARTING,
 					"cpuidle/psci:online",
 					psci_idle_cpuhp_up,
@@ -222,13 +227,16 @@ static int psci_dt_cpu_init_topology(struct cpuidle_driver *drv,
 	if (!psci_has_osi_support())
 		return 0;
 
-	if (IS_ENABLED(CONFIG_PREEMPT_RT))
-		return 0;
-
 	data->dev = dt_idle_attach_cpu(cpu, "psci");
 	if (IS_ERR_OR_NULL(data->dev))
 		return PTR_ERR_OR_ZERO(data->dev);
 
+	psci_cpuidle_use_syscore = true;
+
+	/* The hierarchical topology is limited to s2ram on PREEMPT_RT. */
+	if (IS_ENABLED(CONFIG_PREEMPT_RT))
+		return 0;
+
 	/*
 	 * Using the deepest state for the CPU to trigger a potential selection
 	 * of a shared state for the domain, assumes the domain states are all
@@ -312,6 +320,7 @@ static void psci_cpu_deinit_idle(int cpu)
 	struct psci_cpuidle_data *data = per_cpu_ptr(&psci_cpuidle_data, cpu);
 
 	dt_idle_detach_cpu(data->dev);
+	psci_cpuidle_use_syscore = false;
 	psci_cpuidle_use_cpuhp = false;
 }
 
@@ -408,6 +417,7 @@ static int psci_cpuidle_probe(struct platform_device *pdev)
 			goto out_fail;
 	}
 
+	psci_idle_init_syscore();
 	psci_idle_init_cpuhp();
 	return 0;
 
-- 
2.34.1


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH 6/6] cpuidle: psci: Enable the hierarchical topology for s2idle on PREEMPT_RT

[Ulf Hansson]

To enable the domain-idle-states to be used during s2idle on a PREEMPT_RT
based configuration, let's allow the re-assignment of the ->enter_s2idle()
callback to psci_enter_s2idle_domain_idle_state().

Similar to s2ram, let's leave the support for CPU hotplug outside
PREEMPT_RT, as it's depending on using runtime PM. For s2idle, this means
that an offline CPU's PM domain will remain powered-on. In practise this
may lead to that a shallower idle-state than necessary gets selected, which
shouldn't be an issue (besides wasting power).

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
---
 drivers/cpuidle/cpuidle-psci.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
index ad6ce9fe12b4..2562dc001fc1 100644
--- a/drivers/cpuidle/cpuidle-psci.c
+++ b/drivers/cpuidle/cpuidle-psci.c
@@ -233,18 +233,17 @@ static int psci_dt_cpu_init_topology(struct cpuidle_driver *drv,
 
 	psci_cpuidle_use_syscore = true;
 
-	/* The hierarchical topology is limited to s2ram on PREEMPT_RT. */
-	if (IS_ENABLED(CONFIG_PREEMPT_RT))
-		return 0;
-
 	/*
 	 * Using the deepest state for the CPU to trigger a potential selection
 	 * of a shared state for the domain, assumes the domain states are all
-	 * deeper states.
+	 * deeper states. On PREEMPT_RT the hierarchical topology is limited to
+	 * s2ram and s2idle.
 	 */
-	drv->states[state_count - 1].enter = psci_enter_domain_idle_state;
 	drv->states[state_count - 1].enter_s2idle = psci_enter_s2idle_domain_idle_state;
-	psci_cpuidle_use_cpuhp = true;
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
+		drv->states[state_count - 1].enter = psci_enter_domain_idle_state;
+		psci_cpuidle_use_cpuhp = true;
+	}
 
 	return 0;
 }
-- 
2.34.1


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH 0/6] pmdomain/cpuidle-psci: Support s2idle/s2ram on PREEMPT_RT

[Sebastian Andrzej Siewior]

On 2024-04-29 16:05:25 [+0200], Ulf Hansson wrote:
> The hierarchical PM domain topology and the corresponding domain-idle-states
> are currently disabled on a PREEMPT_RT based configuration. The main reason is
> because spinlocks are turned into sleepable locks on PREEMPT_RT, which means
> genpd and runtime PM can't be use in the atomic idle-path when
> selecting/entering an idle-state.
> 
> For s2idle/s2ram this is an unnecessary limitation that this series intends to
> address. Note that, the support for cpuhotplug is left to future improvements.
> More information about this are available in the commit messages.
> 
> I have tested this on a Dragonboard 410c.

Have you tested this with PREEMPT_RT enabled and if so, which kernel?

> Kind regards
> Ulf Hansson

Sebastian

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH 0/6] pmdomain/cpuidle-psci: Support s2idle/s2ram on PREEMPT_RT

[Ulf Hansson]

On Tue, 30 Apr 2024 at 11:44, Sebastian Andrzej Siewior
<bigeasy@linutronix.de> wrote:
>
> On 2024-04-29 16:05:25 [+0200], Ulf Hansson wrote:
> > The hierarchical PM domain topology and the corresponding domain-idle-states
> > are currently disabled on a PREEMPT_RT based configuration. The main reason is
> > because spinlocks are turned into sleepable locks on PREEMPT_RT, which means
> > genpd and runtime PM can't be use in the atomic idle-path when
> > selecting/entering an idle-state.
> >
> > For s2idle/s2ram this is an unnecessary limitation that this series intends to
> > address. Note that, the support for cpuhotplug is left to future improvements.
> > More information about this are available in the commit messages.
> >
> > I have tested this on a Dragonboard 410c.
>
> Have you tested this with PREEMPT_RT enabled and if so, which kernel?

Yes, of course. :-) I should have mentioned this in the cover-letter, sorry.

I have used the linux-rt-devel.git, which had a branch based upon
v6.8-rc7 a while ago, that I used when I did my tests.

The series needed a small rebase on top of my linux-pm tree [1],
before I could post it though. I also tested the rebased series, but
then of course then not with PREEMPT_RT, but to make sure there are no
regressions.

Kind regards
Uffe

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/ulfh/linux-pm.git next

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel