[PATCH] lib: sbi: Use hsm stop for hsm wait

[Nick Hu]

If we hotplug a core and then perform a suspend-to-RAM operation on a
multi-core platform, the hotplugged CPU may be woken up along with the rest
of the system, particularly on platforms that wake all cores from the
deepest sleep state. When this happens, the hotplugged CPU enters the
sbi_hsm_wait WFI wait loop instead of transitioning into a
platform-specific low-power state. To address this, we add a HSM stop call
within the wait loop. This allows platforms that support HSM stop to enter
a low-power state when the CPU is unexpectedly woken up.

Signed-off-by: Nick Hu <nick.hu at sifive.com>
Reviewed-by: Samuel Holland <samuel.holland at sifive.com>
---
 lib/sbi/sbi_hsm.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/lib/sbi/sbi_hsm.c b/lib/sbi/sbi_hsm.c
index dfe8408d..e8128a39 100644
--- a/lib/sbi/sbi_hsm.c
+++ b/lib/sbi/sbi_hsm.c
@@ -37,6 +37,8 @@
 
 static const struct sbi_hsm_device *hsm_dev = NULL;
 static unsigned long hart_data_offset;
+static bool hsm_device_has_hart_hotplug(void);
+static int hsm_device_hart_stop(void);
 
 /** Per hart specific data to manage state transition **/
 struct sbi_hsm_data {
@@ -170,6 +172,13 @@ static void sbi_hsm_hart_wait(struct sbi_scratch *scratch)
 
 	/* Wait for state transition requested by sbi_hsm_hart_start() */
 	while (atomic_read(&hdata->state) != SBI_HSM_STATE_START_PENDING) {
+		/*
+		 * If the hsm_dev is ready and it support the hotplug, we can
+		 * use the hsm stop for more power saving
+		 */
+		if (hsm_device_has_hart_hotplug())
+			hsm_device_hart_stop();
+
 		wfi();
 	}
 
-- 
2.17.1