MLK-19047-1 ARM: imx: busfreq: Add debug check for double notify

The only user of busfreq notifiers is imx_thermal and if it receives a
double LOW_BUSFREQ_ENTER it will incorrectly decrease the reference
count on its clk. Since tempmon uses pll3 directly this can cause
problems like uart hangs.

Guard against this scenario with an explicit check and warn inside
busfreq_notify. This is not a high-performance path so it's better to be
safe.

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Acked-by: Anson Huang <Anson.Huang@nxp.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/arch/arm/mach-imx/busfreq-imx.c b/arch/arm/mach-imx/busfreq-imx.c
index 353795cec5f4..3e68df65f068 100644
--- a/arch/arm/mach-imx/busfreq-imx.c
+++ b/arch/arm/mach-imx/busfreq-imx.c
@@ -139,10 +139,19 @@ static bool check_m4_sleep(void)
 	return  true;
 }
 
+static bool busfreq_notified_low = false;
+
 static int busfreq_notify(enum busfreq_event event)
 {
 	int ret;
 
+	if (event == LOW_BUSFREQ_ENTER) {
+		WARN_ON(busfreq_notified_low);
+		busfreq_notified_low = true;
+	} else if (event == LOW_BUSFREQ_EXIT) {
+		WARN_ON(!busfreq_notified_low);
+		busfreq_notified_low = false;
+	}
 	ret = raw_notifier_call_chain(&busfreq_notifier_chain, event, NULL);
 
 	return notifier_to_errno(ret);