mfd: tps65219: Implement LOCK register handling for TPS65214

The TPS65214 PMIC variant has a LOCK_REG register that prevents writes to
nearly all registers when locked. Unlock the registers at probe time and
leave them unlocked permanently.

This approach is justified because:
- Register locking is very uncommon in typical system operation
- No code path is expected to lock the registers during runtime
- Adding a custom regmap write function would add overhead to every
  register write, including voltage changes triggered by CPU OPP
  transitions from the cpufreq governor which could happen quite
  frequently

Cc: stable@vger.kernel.org
Fixes: 7947219 ("mfd: tps65219: Add support for TI TPS65214 PMIC")
Reviewed-by: Andrew Davis <afd@ti.com>
Signed-off-by: Kory Maincent (TI.com) <kory.maincent@bootlin.com>
Link: https://patch.msgid.link/20251218-fix_tps65219-v5-1-8bb511417f3a@bootlin.com
Signed-off-by: Lee Jones <lee@kernel.org>

Author: kmaincent

drivers/mfd/tps65219.c

@@ -498,6 +498,15 @@ static int tps65219_probe(struct i2c_client *client)
 		return ret;
 	}
 
+	if (chip_id == TPS65214) {
+		ret = i2c_smbus_write_byte_data(client, TPS65214_REG_LOCK,
+						TPS65214_LOCK_ACCESS_CMD);
+		if (ret) {
+			dev_err(tps->dev, "Failed to unlock registers %d\n", ret);
+			return ret;
+		}
+	}
+
 	ret = devm_regmap_add_irq_chip(tps->dev, tps->regmap, client->irq,
 				       IRQF_ONESHOT, 0, pmic->irq_chip,
 				       &tps->irq_data);

include/linux/mfd/tps65219.h

@@ -149,6 +149,8 @@ enum pmic_id {
 #define TPS65215_ENABLE_LDO2_EN_MASK                    BIT(5)
 #define TPS65214_ENABLE_LDO1_EN_MASK			BIT(5)
 #define TPS65219_ENABLE_LDO4_EN_MASK			BIT(6)
+/* Register Unlock */
+#define TPS65214_LOCK_ACCESS_CMD			0x5a
 /* power ON-OFF sequence slot */
 #define TPS65219_BUCKS_LDOS_SEQUENCE_OFF_SLOT_MASK	GENMASK(3, 0)
 #define TPS65219_BUCKS_LDOS_SEQUENCE_ON_SLOT_MASK	GENMASK(7, 4)