From 4d7e9134bb1f9745229a350b5a3014af64650012 Mon Sep 17 00:00:00 2001
From: Mitchell Horne <mhorne@FreeBSD.org>
Date: Fri, 1 May 2020 21:59:47 +0000
Subject: [PATCH] Use the HSM SBI extension to halt CPUs

Differential Revision:	https://reviews.freebsd.org/D24498
---
 sys/riscv/riscv/machdep.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/sys/riscv/riscv/machdep.c b/sys/riscv/riscv/machdep.c
index 109337230db3..9dacd4b9d3a1 100644
--- a/sys/riscv/riscv/machdep.c
+++ b/sys/riscv/riscv/machdep.c
@@ -473,9 +473,16 @@ void
 cpu_halt(void)
 {
 
+	/*
+	 * Try to power down using the HSM SBI extension and fall back to a
+	 * simple wfi loop.
+	 */
 	intr_disable();
+	if (sbi_probe_extension(SBI_EXT_ID_HSM) != 0)
+		sbi_hsm_hart_stop();
 	for (;;)
 		__asm __volatile("wfi");
+	/* NOTREACHED */
 }
 
 /*