linux-kernel - [PATCH 4/5] irqchip/timer-clint: Use wmb() to order normal writes and IPI writes

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Message-Id: <20250113150933.65121-5-luxu.kernel@bytedance.com>
Date: Mon, 13 Jan 2025 23:09:32 +0800
From: Xu Lu <luxu.kernel@...edance.com>
To: daniel.lezcano@...aro.org,
	tglx@...utronix.de,
	anup@...infault.org,
	paul.walmsley@...ive.com,
	palmer@...belt.com
Cc: lihangjing@...edance.com,
	xieyongji@...edance.com,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Xu Lu <luxu.kernel@...edance.com>
Subject: [PATCH 4/5] irqchip/timer-clint: Use wmb() to order normal writes and IPI writes

During an IPI procedure, we need to ensure all previous write operations
are visible to other CPUs before sending a real IPI. We use wmb() barrier
to ensure this as CLINT issues IPI via mmio writes.

Signed-off-by: Xu Lu <luxu.kernel@...edance.com>
---
 drivers/clocksource/timer-clint.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
index 0bdd9d7ec545..8d73b45f9966 100644
--- a/drivers/clocksource/timer-clint.c
+++ b/drivers/clocksource/timer-clint.c
@@ -48,6 +48,12 @@ EXPORT_SYMBOL(clint_time_val);
 #ifdef CONFIG_SMP
 static void clint_send_ipi(unsigned int cpu)
 {
+	/*
+	 * Ensure that stores to normal memory are visible to the other CPUs
+	 * before issuing IPI.
+	 */
+	wmb();
+
 	writel(1, clint_ipi_base + cpuid_to_hartid_map(cpu));
 }
 
-- 
2.20.1