NFC: trf7970a: Set correct Vin voltage in Chip Status Control register

Currently, the trf7970a driver assumes that the Vin voltage is 5V when
it writes to the 'Chip Status Control' register. That may not be correct
so use the regulator facility to get the Vin voltage and set the VRS5_3
bit correctly when writing to that register.
Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/nfc/trf7970a.c

@@ -336,6 +336,7 @@ struct trf7970a {
 	struct sk_buff			*rx_skb;
 	nfc_digital_cmd_complete_t	cb;
 	void				*cb_arg;
+	u8				chip_status_ctrl;
 	u8				iso_ctrl;
 	u8				iso_ctrl_tech;
 	u8				modulator_sys_clk_ctrl;
@@ -779,8 +780,7 @@ static int trf7970a_init(struct trf7970a *trf)
 	trf->special_fcn_reg1 = 0;
 
 	ret = trf7970a_write(trf, TRF7970A_CHIP_STATUS_CTRL,
-			TRF7970A_CHIP_STATUS_RF_ON |
-				TRF7970A_CHIP_STATUS_VRS5_3);
+			trf->chip_status_ctrl | TRF7970A_CHIP_STATUS_RF_ON);
 	if (ret)
 		goto err_out;
 
@@ -1245,7 +1245,7 @@ static int trf7970a_probe(struct spi_device *spi)
 	struct device_node *np = spi->dev.of_node;
 	const struct spi_device_id *id = spi_get_device_id(spi);
 	struct trf7970a *trf;
-	int ret;
+	int uvolts, ret;
 
 	if (!np) {
 		dev_err(&spi->dev, "No Device Tree entry\n");
@@ -1315,6 +1315,11 @@ static int trf7970a_probe(struct spi_device *spi)
 		goto err_destroy_lock;
 	}
 
+	uvolts = regulator_get_voltage(trf->regulator);
+
+	if (uvolts > 4000000)
+		trf->chip_status_ctrl = TRF7970A_CHIP_STATUS_VRS5_3;
+
 	trf->powering_up = true;
 
 	trf->ddev = nfc_digital_allocate_device(&trf7970a_nfc_ops,