NFC: trf7970a: Add device tree option of 1.8 Volt IO voltage

The TRF7970A has configuration options for supporting hardware designs
with 1.8 Volt or 3.3 Volt IO.   This commit adds a device tree option,
using a fixed regulator binding, for setting the io voltage to match
the hardware configuration. If no option is supplied it defaults to
3.3 volt configuration.
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Geoff Lansberry <geoff@kuvee.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

Documentation/devicetree/bindings/net/nfc/trf7970a.txt

@@ -21,6 +21,7 @@ Optional SoC Specific Properties:
 - t5t-rmb-extra-byte-quirk: Specify that the trf7970a has the erratum
   where an extra byte is returned by Read Multiple Block commands issued
   to Type 5 tags.
+- vdd-io-supply: Regulator specifying voltage for vdd-io
 - clock-frequency: Set to specify that the input frequency to the trf7970a is 13560000Hz or 27120000Hz
 
 Example (for ARM-based BeagleBone with TRF7970A on SPI1):
@@ -40,6 +41,7 @@ Example (for ARM-based BeagleBone with TRF7970A on SPI1):
 				  <&gpio2 5 GPIO_ACTIVE_LOW>;
 		vin-supply = <&ldo3_reg>;
 		vin-voltage-override = <5000000>;
+		vdd-io-supply = <&ldo2_reg>;
 		autosuspend-delay = <30000>;
 		irq-status-read-quirk;
 		en2-rf-quirk;

drivers/nfc/trf7970a.c

@@ -444,6 +444,7 @@ struct trf7970a {
 	u8				iso_ctrl_tech;
 	u8				modulator_sys_clk_ctrl;
 	u8				special_fcn_reg1;
+	u8				io_ctrl;
 	unsigned int			guard_time;
 	int				technology;
 	int				framing;
@@ -1051,6 +1052,11 @@ static int trf7970a_init(struct trf7970a *trf)
 	if (ret)
 		goto err_out;
 
+	ret = trf7970a_write(trf, TRF7970A_REG_IO_CTRL,
+			trf->io_ctrl | TRF7970A_REG_IO_CTRL_VRS(0x1));
+	if (ret)
+		goto err_out;
+
 	ret = trf7970a_write(trf, TRF7970A_NFC_TARGET_LEVEL, 0);
 	if (ret)
 		goto err_out;
@@ -1767,7 +1773,7 @@ static int _trf7970a_tg_listen(struct nfc_digital_dev *ddev, u16 timeout,
 		goto out_err;
 
 	ret = trf7970a_write(trf, TRF7970A_REG_IO_CTRL,
-			TRF7970A_REG_IO_CTRL_VRS(0x1));
+			trf->io_ctrl | TRF7970A_REG_IO_CTRL_VRS(0x1));
 	if (ret)
 		goto out_err;
 
@@ -2107,6 +2113,24 @@ static int trf7970a_probe(struct spi_device *spi)
 	if (uvolts > 4000000)
 		trf->chip_status_ctrl = TRF7970A_CHIP_STATUS_VRS5_3;
 
+	trf->regulator = devm_regulator_get(&spi->dev, "vdd-io");
+	if (IS_ERR(trf->regulator)) {
+		ret = PTR_ERR(trf->regulator);
+		dev_err(trf->dev, "Can't get VDD_IO regulator: %d\n", ret);
+		goto err_destroy_lock;
+	}
+
+	ret = regulator_enable(trf->regulator);
+	if (ret) {
+		dev_err(trf->dev, "Can't enable VDD_IO: %d\n", ret);
+		goto err_destroy_lock;
+	}
+
+	if (regulator_get_voltage(trf->regulator) == 1800000) {
+		trf->io_ctrl = TRF7970A_REG_IO_CTRL_IO_LOW;
+		dev_dbg(trf->dev, "trf7970a config vdd_io to 1.8V\n");
+	}
+
 	trf->ddev = nfc_digital_allocate_device(&trf7970a_nfc_ops,
 			TRF7970A_SUPPORTED_PROTOCOLS,
 			NFC_DIGITAL_DRV_CAPS_IN_CRC |