pmdomain: Respect the CPU system wakeup QoS limit for s2idle

A CPU system wakeup QoS limit may have been requested by user space. To
avoid breaking this constraint when entering a low power state during
s2idle through genpd, let's extend the corresponding genpd governor for
CPUs. More precisely, during s2idle let the genpd governor select a
suitable domain idle state, by taking into account the QoS limit.

Reviewed-by: Dhruva Gole <[e-mail]>
Reviewed-by: Kevin Hilman (TI) <[e-mail]>
Tested-by: Kevin Hilman (TI) <[e-mail]>
Signed-off-by: Ulf Hansson <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/pmdomain/core.c

···
 			return;
 	}
 
-	/* Choose the deepest state when suspending */
-	genpd->state_idx = genpd->state_count - 1;
+	if (genpd->gov && genpd->gov->system_power_down_ok) {
+		if (!genpd->gov->system_power_down_ok(&genpd->domain))
+			return;
+	} else {
+		/* Default to the deepest state. */
+		genpd->state_idx = genpd->state_count - 1;
+	}
+
 	if (_genpd_power_off(genpd, false)) {
 		genpd->states[genpd->state_idx].rejected++;
 		return;

drivers/pmdomain/governor.c

···
 	return false;
 }
 
+static bool cpu_system_power_down_ok(struct dev_pm_domain *pd)
+{
+	s64 constraint_ns = cpu_wakeup_latency_qos_limit() * NSEC_PER_USEC;
+	struct generic_pm_domain *genpd = pd_to_genpd(pd);
+	int state_idx = genpd->state_count - 1;
+
+	if (!(genpd->flags & GENPD_FLAG_CPU_DOMAIN)) {
+		genpd->state_idx = state_idx;
+		return true;
+	}
+
+	/* Find the deepest state for the latency constraint. */
+	while (state_idx >= 0) {
+		s64 latency_ns = genpd->states[state_idx].power_off_latency_ns +
+				 genpd->states[state_idx].power_on_latency_ns;
+
+		if (latency_ns <= constraint_ns) {
+			genpd->state_idx = state_idx;
+			return true;
+		}
+		state_idx--;
+	}
+
+	return false;
+}
+
 struct dev_power_governor pm_domain_cpu_gov = {
 	.suspend_ok = default_suspend_ok,
 	.power_down_ok = cpu_power_down_ok,
+	.system_power_down_ok = cpu_system_power_down_ok,
 };
 #endif
 

include/linux/pm_domain.h

···
 };
 
 struct dev_power_governor {
+	bool (*system_power_down_ok)(struct dev_pm_domain *domain);
 	bool (*power_down_ok)(struct dev_pm_domain *domain);
 	bool (*suspend_ok)(struct device *dev);
 };