iio: amplifiers: ad8366: Add support for ADL5240 VGA

The ADL5240 is a high performance, digitally controlled variable gain
amplifier (VGA) operating from 100 MHz to 4000 MHz. The VGA integrates a
high performance, 20 dB gain, internally matched amplifier (AMP) with a
6-bit digital step attenuator (DSA) that has a gain control range of
31.5 dB in 0.5 dB steps with ±0.25 dB step accuracy.

Datasheet link:
  https://www.analog.com/media/en/technical-documentation/data-sheets/adl5240.pdf

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/amplifiers/Kconfig

@@ -17,6 +17,7 @@ config AD8366
 	  from Analog Devices:
 	    AD8366 Dual-Digital Variable Gain Amplifier (VGA)
 	    ADA4961 BiCMOS RF Digital Gain Amplifier (DGA)
+	    ADL5240 Digitally controlled variable gain amplifier (VGA)
 
 	  To compile this driver as a module, choose M here: the
 	  module will be called ad8366.

drivers/iio/amplifiers/ad8366.c

@@ -4,6 +4,7 @@
  * This driver supports the following gain amplifiers:
  *   AD8366 Dual-Digital Variable Gain Amplifier (VGA)
  *   ADA4961 BiCMOS RF Digital Gain Amplifier (DGA)
+ *   ADL5240 Digitally controlled variable gain amplifier (VGA)
  *
  * Copyright 2012-2019 Analog Devices Inc.
  */
@@ -25,6 +26,7 @@
 enum ad8366_type {
 	ID_AD8366,
 	ID_ADA4961,
+	ID_ADL5240,
 };
 
 struct ad8366_info {
@@ -56,6 +58,10 @@ static struct ad8366_info ad8366_infos[] = {
 		.gain_min = -6000,
 		.gain_max = 15000,
 	},
+	[ID_ADL5240] = {
+		.gain_min = -11500,
+		.gain_max = 20000,
+	},
 };
 
 static int ad8366_write(struct iio_dev *indio_dev,
@@ -75,6 +81,9 @@ static int ad8366_write(struct iio_dev *indio_dev,
 	case ID_ADA4961:
 		st->data[0] = ch_a & 0x1F;
 		break;
+	case ID_ADL5240:
+		st->data[0] = (ch_a & 0x3F);
+		break;
 	}
 
 	ret = spi_write(st->spi, st->data, indio_dev->num_channels);
@@ -106,6 +115,9 @@ static int ad8366_read_raw(struct iio_dev *indio_dev,
 		case ID_ADA4961:
 			gain = 15000 - code * 1000;
 			break;
+		case ID_ADL5240:
+			gain = 20000 - 31500 + code * 500;
+			break;
 		}
 
 		/* Values in dB */
@@ -149,6 +161,9 @@ static int ad8366_write_raw(struct iio_dev *indio_dev,
 	case ID_ADA4961:
 		code = (15000 - gain) / 1000;
 		break;
+	case ID_ADL5240:
+		code = ((gain - 500 - 20000) / 500) & 0x3F;
+		break;
 	}
 
 	mutex_lock(&st->lock);
@@ -217,6 +232,7 @@ static int ad8366_probe(struct spi_device *spi)
 		indio_dev->num_channels = ARRAY_SIZE(ad8366_channels);
 		break;
 	case ID_ADA4961:
+	case ID_ADL5240:
 		st->reset_gpio = devm_gpiod_get(&spi->dev, "reset",
 			GPIOD_OUT_HIGH);
 		indio_dev->channels = ada4961_channels;
@@ -268,6 +284,7 @@ static int ad8366_remove(struct spi_device *spi)
 static const struct spi_device_id ad8366_id[] = {
 	{"ad8366",  ID_AD8366},
 	{"ada4961", ID_ADA4961},
+	{"adl5240", ID_ADL5240},
 	{}
 };
 MODULE_DEVICE_TABLE(spi, ad8366_id);