PM / devfreq: mediatek: protect oop in critical session

mtk_ccifreq_opp_notifier is reenter function when policy0 / policy6
change freq, so mutex_lock should protect all OPP event.

Link: https://lore.kernel.org/lkml/20230818021741.6173-1-chun-jen.tseng@mediatek.com/T/Signed-off-by: Mark Tseng <chun-jen.tseng@mediatek.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

drivers/devfreq/mtk-cci-devfreq.c

@@ -137,6 +137,8 @@ static int mtk_ccifreq_target(struct device *dev, unsigned long *freq,
 	if (drv->pre_freq == *freq)
 		return 0;
 
+	mutex_lock(&drv->reg_lock);
+
 	inter_voltage = drv->inter_voltage;
 	cci_pll = clk_get_parent(drv->cci_clk);
 
@@ -147,8 +149,6 @@ static int mtk_ccifreq_target(struct device *dev, unsigned long *freq,
 		return PTR_ERR(opp);
 	}
 
-	mutex_lock(&drv->reg_lock);
-
 	voltage = dev_pm_opp_get_voltage(opp);
 	dev_pm_opp_put(opp);
 
@@ -227,9 +227,9 @@ static int mtk_ccifreq_opp_notifier(struct notifier_block *nb,
 	drv = container_of(nb, struct mtk_ccifreq_drv, opp_nb);
 
 	if (event == OPP_EVENT_ADJUST_VOLTAGE) {
+		mutex_lock(&drv->reg_lock);
 		freq = dev_pm_opp_get_freq(opp);
 
-		mutex_lock(&drv->reg_lock);
 		/* current opp item is changed */
 		if (freq == drv->pre_freq) {
 			volt = dev_pm_opp_get_voltage(opp);