pmdomain: core: Enable s2idle for CPU PM domains on PREEMPT_RT

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>
Tested-by: Raghavendra Kakarla <quic_rkakarla@quicinc.com>  # qcm6490 with PREEMPT_RT set
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20240527142557.321610-2-ulf.hansson@linaro.org

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)
@@ -2143,7 +2185,10 @@ static void genpd_free_data(struct generic_pm_domain *genpd)
 
 static void genpd_lock_init(struct generic_pm_domain *genpd)
 {
-	if (genpd_is_irq_safe(genpd)) {
+	if (genpd_is_cpu_domain(genpd)) {
+		raw_spin_lock_init(&genpd->raw_slock);
+		genpd->lock_ops = &genpd_raw_spin_ops;
+	} else if (genpd_is_irq_safe(genpd)) {
 		spin_lock_init(&genpd->slock);
 		genpd->lock_ops = &genpd_spin_ops;
 	} else {

include/linux/pm_domain.h

@@ -198,8 +198,11 @@ 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)