linux-kernel - [PATCH 2/3] arm64: smp: Implement cpus_has_pending

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Message-ID: <20251003150251.520624-3-ulf.hansson@linaro.org>
Date: Fri,  3 Oct 2025 17:02:44 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: "Rafael J . Wysocki" <rafael@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Thomas Gleixner <tglx@...utronix.de>
Cc: Maulik Shah <quic_mkshah@...cinc.com>,
	Sudeep Holla <sudeep.holla@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-pm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Ulf Hansson <ulf.hansson@...aro.org>
Subject: [PATCH 2/3] arm64: smp: Implement cpus_has_pending_ipi()

To add support for keeping track of whether there may be a pending IPI
scheduled for a CPU or a group of CPUs, let's implement
cpus_has_pending_ipi() for arm64.

Note, the implementation is intentionally lightweight and doesn't use any
additional lock. This is good enough for cpuidle based decisions.

Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
---
 arch/arm64/kernel/smp.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 68cea3a4a35c..dd1acfa91d44 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -55,6 +55,8 @@
 
 #include <trace/events/ipi.h>
 
+static DEFINE_PER_CPU(bool, pending_ipi);
+
 /*
  * as from 2.5, kernels no longer have an init_tasks structure
  * so we need some other way of telling a new secondary core
@@ -1012,6 +1014,8 @@ static void do_handle_IPI(int ipinr)
 
 	if ((unsigned)ipinr < NR_IPI)
 		trace_ipi_exit(ipi_types[ipinr]);
+
+	per_cpu(pending_ipi, cpu) = false;
 }
 
 static irqreturn_t ipi_handler(int irq, void *data)
@@ -1024,10 +1028,26 @@ static irqreturn_t ipi_handler(int irq, void *data)
 
 static void smp_cross_call(const struct cpumask *target, unsigned int ipinr)
 {
+	unsigned int cpu;
+
+	for_each_cpu(cpu, target)
+		per_cpu(pending_ipi, cpu) = true;
+
 	trace_ipi_raise(target, ipi_types[ipinr]);
 	arm64_send_ipi(target, ipinr);
 }
 
+bool cpus_has_pending_ipi(const struct cpumask *mask)
+{
+	unsigned int cpu;
+
+	for_each_cpu(cpu, mask) {
+		if (per_cpu(pending_ipi, cpu))
+			return true;
+	}
+	return false;
+}
+
 static bool ipi_should_be_nmi(enum ipi_msg_type ipi)
 {
 	if (!system_uses_irq_prio_masking())
-- 
2.43.0