[PATCH v7 3/3] ARM: Check if a CPU has gone offline

[Ashwin Chaugule]

PSCIv0.2 adds a new function called AFFINITY_INFO, which
can be used to query if a specified CPU has actually gone
offline. Calling this function via cpu_kill ensures that
a CPU has quiesced after a call to cpu_die.

Signed-off-by: Ashwin Chaugule <ashwin.chaugule at linaro.org>
Reviewed-by: Rob Herring <robh at kernel.org>
---
 arch/arm/kernel/psci_smp.c | 32 ++++++++++++++++++++++++++++++++
 include/uapi/linux/psci.h  |  5 +++++
 2 files changed, 37 insertions(+)

diff --git a/arch/arm/kernel/psci_smp.c b/arch/arm/kernel/psci_smp.c
index 570a48c..0b1882b 100644
--- a/arch/arm/kernel/psci_smp.c
+++ b/arch/arm/kernel/psci_smp.c
@@ -16,6 +16,8 @@
 #include <linux/init.h>
 #include <linux/smp.h>
 #include <linux/of.h>
+#include <linux/delay.h>
+#include <uapi/linux/psci.h>
 
 #include <asm/psci.h>
 #include <asm/smp_plat.h>
@@ -66,6 +68,35 @@ void __ref psci_cpu_die(unsigned int cpu)
        /* We should never return */
        panic("psci: cpu %d failed to shutdown\n", cpu);
 }
+
+int __ref psci_cpu_kill(unsigned int cpu)
+{
+	int err, retry = 0;
+
+	if (!psci_ops.affinity_info)
+		return 1;
+	/*
+	 * cpu_kill could race with cpu_die and we can
+	 * potentially end up declaring this cpu undead
+	 * while it is dying. So, try once more if it fails.
+	 */
+retry_once:
+	err = psci_ops.affinity_info(cpu_logical_map(cpu), 0);
+
+	if (err != PSCI_AFFINITY_INFO_RET_OFF) {
+		if (!retry++) {
+			msleep(100);
+			pr_info("Retrying once more to check for CPU kill\n");
+			goto retry_once;
+		}
+		pr_err("psci: Cannot kill CPU:%d, psci ret val: %d\n",
+				cpu, err);
+		/* Make platform_cpu_kill() fail. */
+		return 0;
+	}
+	return 1;
+}
+
 #endif
 
 bool __init psci_smp_available(void)
@@ -78,5 +109,6 @@ struct smp_operations __initdata psci_smp_ops = {
 	.smp_boot_secondary	= psci_boot_secondary,
 #ifdef CONFIG_HOTPLUG_CPU
 	.cpu_die		= psci_cpu_die,
+	.cpu_kill		= psci_cpu_kill,
 #endif
 };
diff --git a/include/uapi/linux/psci.h b/include/uapi/linux/psci.h
index a4136c3..857209b 100644
--- a/include/uapi/linux/psci.h
+++ b/include/uapi/linux/psci.h
@@ -74,4 +74,9 @@
 #define PSCI_RET_NOT_PRESENT			-7
 #define PSCI_RET_DISABLED			-8
 
+/* Return values from the PSCI_ID_AFFINITY_INFO Function. */
+#define PSCI_AFFINITY_INFO_RET_ON			0
+#define PSCI_AFFINITY_INFO_RET_OFF			1
+#define PSCI_AFFINITY_INFO_RET_ON_PENDING	2
+
 #endif /* _UAPI_LINUX_PSCI_H */
-- 
1.8.3.2