power: reset: sc27xx: Power off the external subsystems' connection

When powering off the whole system, we should power off some external
subsystems' connection firstly, otherwise some external subsystems
will hold some power and result in powering down abnormally.
Signed-off-by: Sherry Zong <sherry.zong@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang7@gmail.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/reset/sc27xx-poweroff.c

@@ -13,6 +13,8 @@
 
 #define SC27XX_PWR_PD_HW	0xc2c
 #define SC27XX_PWR_OFF_EN	BIT(0)
+#define SC27XX_SLP_CTRL		0xdf0
+#define SC27XX_LDO_XTL_EN	BIT(3)
 
 static struct regmap *regmap;
 
@@ -40,6 +42,9 @@ static struct syscore_ops poweroff_syscore_ops = {
 
 static void sc27xx_poweroff_do_poweroff(void)
 {
+	/* Disable the external subsys connection's power firstly */
+	regmap_write(regmap, SC27XX_SLP_CTRL, SC27XX_LDO_XTL_EN);
+
 	regmap_write(regmap, SC27XX_PWR_PD_HW, SC27XX_PWR_OFF_EN);
 }