regulator: act8945a-regulator: unlock expert registers

Unlock expert registers for act8945a.
This is based on orginal work of Boris Brezillon at [1].

[1] https://www.spinics.net/lists/kernel/msg2942960.html

Signed-off-by: Claudiu Beznea <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/regulator/act8945a-regulator.c

···
 #include <linux/module.h>
 #include <linux/of_device.h>
 #include <linux/platform_device.h>
+#include <linux/regmap.h>
 #include <linux/regulator/driver.h>
 #include <linux/regulator/machine.h>
 
···
  */
 #define ACT8945A_SYS_MODE	0x00
 #define ACT8945A_SYS_CTRL	0x01
+#define ACT8945A_SYS_UNLK_REGS	0x0b
 #define ACT8945A_DCDC1_VSET1	0x20
 #define ACT8945A_DCDC1_VSET2	0x21
 #define ACT8945A_DCDC1_CTRL	0x22
···
 	struct regulator_config config = { };
 	const struct regulator_desc *regulators;
 	struct regulator_dev *rdev;
+	struct regmap *regmap;
 	int i, num_regulators;
 	bool voltage_select;
+
+	regmap = dev_get_regmap(pdev->dev.parent, NULL);
+	if (!regmap) {
+		dev_err(&pdev->dev,
+			"could not retrieve regmap from parent device\n");
+		return -EINVAL;
+	}
 
 	voltage_select = of_property_read_bool(pdev->dev.parent->of_node,
 					       "active-semi,vsel-high");
···
 		}
 	}
 
-	return 0;
+	/* Unlock expert registers. */
+	return regmap_write(regmap, ACT8945A_SYS_UNLK_REGS, 0xef);
 }
 
 static struct platform_driver act8945a_pmic_driver = {