ARM: bL_switcher: synchronize the outbound with the inbound

Let's wait for the inbound to come up and snoop some of the outbound
cache. That should be a bit more efficient than going down right away.
Monitoring the CCI event counters could be a better approach eventually.

Signed-off-by: Nicolas Pitre <nico@linaro.org>

1 files changed, 22 insertions, 2 deletions

diff --git a/arch/arm/common/bL_switcher.c b/arch/arm/common/bL_switcher.c
index e379c918f08..0de28f101b7 100644
--- a/arch/arm/common/bL_switcher.c
+++ b/arch/arm/common/bL_switcher.c
@@ -52,9 +52,10 @@ static int read_mpidr(void)
  * bL switcher core code.
  */
 
-static void bL_do_switch(void *_unused)
+static void bL_do_switch(void *_arg)
 {
 	unsigned ib_mpidr, ib_cpu, ib_cluster;
+	long volatile handshake, **handshake_ptr = _arg;
 
 	pr_debug("%s\n", __func__);
 
@@ -62,6 +63,13 @@ static void bL_do_switch(void *_unused)
 	ib_cpu = MPIDR_AFFINITY_LEVEL(ib_mpidr, 0);
 	ib_cluster = MPIDR_AFFINITY_LEVEL(ib_mpidr, 1);
 
+	/* Advertise our handshake location */
+	if (handshake_ptr) {
+		handshake = 0;
+		*handshake_ptr = &handshake;
+	} else
+		handshake = -1;
+
 	/*
 	 * Our state has been saved at this point.  Let's release our
 	 * inbound CPU.
@@ -80,6 +88,14 @@ static void bL_do_switch(void *_unused)
 	 * we have none.
 	 */
 
+	/*
+	 * Let's wait until our inbound is alive.
+	 */
+	while (!handshake) {
+		wfe();
+		smp_mb();
+	}
+
 	/* Let's put ourself down. */
 	mcpm_cpu_power_down();
 
@@ -127,6 +143,7 @@ static int bL_switch_to(unsigned int new_cluster_id)
 	unsigned int ob_mpidr, ob_cpu, ob_cluster, ib_mpidr, ib_cpu, ib_cluster;
 	struct tick_device *tdev;
 	enum clock_event_mode tdev_mode;
+	long volatile *handshake_ptr;
 	int ret;
 
 	this_cpu = smp_processor_id();
@@ -200,7 +217,7 @@ static int bL_switch_to(unsigned int new_cluster_id)
 	sync_cache_w(&cpu_logical_map(this_cpu));
 
 	/* Let's do the actual CPU switch. */
-	ret = cpu_suspend(0, bL_switchpoint);
+	ret = cpu_suspend((unsigned long)&handshake_ptr, bL_switchpoint);
 	if (ret > 0)
 		panic("%s: cpu_suspend() returned %d\n", __func__, ret);
 
@@ -222,6 +239,9 @@ static int bL_switch_to(unsigned int new_cluster_id)
 	local_fiq_enable();
 	local_irq_enable();
 
+	*handshake_ptr = 1;
+	dsb_sev();
+
 	if (ret)
 		pr_err("%s exiting with error %d\n", __func__, ret);
 	return ret;