[PATCH v2 6/6] iio: adc: ti-ads1298: add ADS1299 support

[Stephan Costa Barros <stephanbrrs8@gmail.com>]

The ADS1299, ADS1299-6 and ADS1299-4 are 8, 6 and 4-channel, 24-bit
biopotential ADCs for EEG. They share the register map, the commands
and the data format of the ADS129x, and differ in:

- the PGA gains, 1, 2, 4, 6, 8, 12 and 24;
- the data rates, f_CLK / 2^(7 + DR) with no HR bit, from 16 kSPS to
  250 SPS, and the oversampling ratio, 64 * 2^DR;
- the internal reference, a fixed 4.5 V, and the reserved bits 6:5 of
  CONFIG3;
- the ID register, which holds the channel count in bits 1:0;
- the register map, which ends at CONFIG4;
- the inputs, which are shorted out of reset.

Add the chip info for the ADS1299, and connect the inputs of every
channel at init, which changes nothing on the ADS129x, whose inputs are
already connected out of reset. The channel count is read from the ID
register, so ti,ads1299 also serves the ADS1299-4 and ADS1299-6 through
their fallback.

For both families, enable the DVDD supply when the device tree gives
one, and hold PWDN asserted, like RESET, until the supplies and the
clock are up. Nothing changes for a device tree that has neither.

Tested on an ADS1299 with a Raspberry Pi 4.

Signed-off-by: Stephan Costa Barros <stephanbrrs8@gmail.com>
---
 drivers/iio/adc/Kconfig      |   6 +--
 drivers/iio/adc/ti-ads1298.c | 100 +++++++++++++++++++++++++++++++++--
 2 files changed, 100 insertions(+), 6 deletions(-)

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index a29ed8f45..724ae6123 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -1920,14 +1920,14 @@ config TI_ADS1262
 	  called ti-ads1262.
 
 config TI_ADS1298
-	tristate "Texas Instruments ADS1298"
+	tristate "Texas Instruments ADS1298 and ADS1299"
 	depends on SPI
 	select IIO_BUFFER
 	select IIO_KFIFO_BUF
 	select REGMAP
 	help
-	  If you say yes here you get support for Texas Instruments ADS1298
-	  medical ADC chips
+	  If you say yes here you get support for Texas Instruments ADS1294,
+	  ADS1296, ADS1298 and ADS1299 medical ADC chips, and their variants
 
 	  This driver can also be built as a module. If so, the module will be
 	  called ti-ads1298.
diff --git a/drivers/iio/adc/ti-ads1298.c b/drivers/iio/adc/ti-ads1298.c
index 5ad543bdf..e0cea23b1 100644
--- a/drivers/iio/adc/ti-ads1298.c
+++ b/drivers/iio/adc/ti-ads1298.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
-/* TI ADS1298 chip family driver
+/* TI ADS1298 and ADS1299 chip family driver
  * Copyright (C) 2023 - 2024 Topic Embedded Products
+ * Copyright (C) 2026 Stephan Costa Barros <stephanbrrs8@gmail.com>
  */
 
 #include <linux/bitfield.h>
@@ -45,6 +46,10 @@
 #define ADS1298_MASK_ID_CHANNELS		GENMASK(2, 0)
 #define ADS1298_ID_FAMILY_ADS129X		0x90
 #define ADS1298_ID_FAMILY_ADS129XR		0xd0
+/* ADS1299: bit 4 reads 1 and DEV_ID[3:2] is 11; bits 7:5 are the revision */
+#define ADS1299_MASK_ID_DEVICE			GENMASK(4, 2)
+#define ADS1299_MASK_ID_CHANNELS		GENMASK(1, 0)
+#define ADS1299_ID_DEVICE			0x7
 
 #define ADS1298_REG_CONFIG1	0x01
 #define ADS1298_MASK_CONFIG1_HR			BIT(7)
@@ -65,12 +70,14 @@
 #define ADS1298_MASK_CONFIG3_RESERVED		BIT(6)
 #define ADS1298_MASK_CONFIG3_VREF_4V		BIT(5)
 #define ADS1298_VREF_4V_MV			4000
+#define ADS1299_MASK_CONFIG3_RESERVED		GENMASK(6, 5)
 
 #define ADS1298_REG_LOFF	0x04
 #define ADS1298_REG_CHnSET(n)	(0x05 + (n))
 #define ADS1298_MASK_CH_PD		BIT(7)
 #define ADS1298_MASK_CH_PGA		GENMASK(6, 4)
 #define ADS1298_MASK_CH_MUX		GENMASK(2, 0)
+#define ADS1298_MUX_NORMAL		0
 
 #define ADS1298_REG_LOFF_STATP	0x12
 #define ADS1298_REG_LOFF_STATN	0x13
@@ -354,6 +361,15 @@ static int ads1298_set_samp_freq(struct ads1298_private *priv, int val)
 		return -EINVAL;
 
 	factor = (rate >> info->dr_shift) / val;
+
+	if (!info->has_hr) {
+		/* The slowest rate at or above val, or the lowest of all */
+		cfg = factor ? min(ilog2(factor), ADS1298_LOWEST_DR) : 0;
+
+		return regmap_update_bits(priv->regmap, ADS1298_REG_CONFIG1,
+					  ADS1298_MASK_CONFIG1_DR, cfg);
+	}
+
 	if (factor >= BIT(ADS1298_LOWEST_DR + 1))
 		cfg = ADS1298_LOWEST_DR; /* Lowest rate, in LP mode */
 	else if (factor)
@@ -772,6 +788,43 @@ static int ads1298_parse_id(struct iio_dev *indio_dev, unsigned int id)
 	return 0;
 }
 
+/* The ADS1299 has no WCT registers */
+static const struct regmap_config ads1299_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.reg_read = ads1298_reg_read,
+	.reg_write = ads1298_reg_write,
+	.max_register = ADS1298_REG_CONFIG4,
+	.wr_table = &ads1298_regmap_writeable,
+	.volatile_table = &ads1298_regmap_volatile,
+	.cache_type = REGCACHE_MAPLE,
+};
+
+static int ads1299_parse_id(struct iio_dev *indio_dev, unsigned int id)
+{
+	struct ads1298_private *priv = iio_priv(indio_dev);
+	struct device *dev = &priv->spi->dev;
+	unsigned int nu_ch;
+
+	nu_ch = FIELD_GET(ADS1299_MASK_ID_CHANNELS, id);
+	/* 0, 1 and 2 are 4, 6 and 8 channels; 3 is reserved */
+	if (FIELD_GET(ADS1299_MASK_ID_DEVICE, id) != ADS1299_ID_DEVICE ||
+	    nu_ch > 2)
+		return dev_err_probe(dev, -ENODEV, "Unknown ID: 0x%x\n", id);
+	indio_dev->num_channels = 4 + 2 * nu_ch;
+
+	/* TI sells the 8-channel part as plain ADS1299 */
+	if (indio_dev->num_channels == ADS1298_MAX_CHANNELS)
+		indio_dev->name = "ads1299";
+	else
+		indio_dev->name = devm_kasprintf(dev, GFP_KERNEL, "ads1299-%u",
+						 indio_dev->num_channels);
+	if (!indio_dev->name)
+		return -ENOMEM;
+
+	return 0;
+}
+
 static const u8 ads1298_gains[] = { 6, 1, 2, 3, 4, 8, 12 };
 
 static const struct ads1298_chip_info ads1298_chip_info = {
@@ -787,10 +840,24 @@ static const struct ads1298_chip_info ads1298_chip_info = {
 	.config3_reserved = ADS1298_MASK_CONFIG3_RESERVED,
 };
 
+static const u8 ads1299_gains[] = { 1, 2, 4, 6, 8, 12, 24 };
+
+static const struct ads1298_chip_info ads1299_chip_info = {
+	.parse_id = ads1299_parse_id,
+	.regmap_config = &ads1299_regmap_config,
+	.gains = ads1299_gains,
+	.num_gains = ARRAY_SIZE(ads1299_gains),
+	.dr_shift = 7,
+	.osr_base = 64,
+	.vref_mv = 4500,
+	.config3_reserved = ADS1299_MASK_CONFIG3_RESERVED,
+};
+
 static int ads1298_init(struct iio_dev *indio_dev)
 {
 	struct ads1298_private *priv = iio_priv(indio_dev);
 	unsigned int val;
+	unsigned int i;
 	int ret;
 
 	/* Device initializes into RDATAC mode, which we don't want */
@@ -822,6 +889,16 @@ static int ads1298_init(struct iio_dev *indio_dev)
 	if (!priv->reg_vref)
 		msleep(ADS1298_REF_START_UP_MS);
 
+	/* The ADS1299 comes out of reset with its inputs shorted */
+	for (i = 0; i < indio_dev->num_channels; i++) {
+		ret = regmap_update_bits(priv->regmap, ADS1298_REG_CHnSET(i),
+					 ADS1298_MASK_CH_MUX,
+					 FIELD_PREP(ADS1298_MASK_CH_MUX,
+						    ADS1298_MUX_NORMAL));
+		if (ret)
+			return ret;
+	}
+
 	return 0;
 }
 
@@ -830,6 +907,7 @@ static int ads1298_probe(struct spi_device *spi)
 	struct ads1298_private *priv;
 	struct iio_dev *indio_dev;
 	struct device *dev = &spi->dev;
+	struct gpio_desc *powerdown_gpio;
 	struct gpio_desc *reset_gpio;
 	unsigned long clk_rate;
 	int ret;
@@ -844,12 +922,18 @@ static int ads1298_probe(struct spi_device *spi)
 	if (!priv->chip_info)
 		return -ENODEV;
 
-	/* Reset to be asserted before enabling clock and power */
+	/* Reset and power-down to be asserted before enabling clock and power */
 	reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
 	if (IS_ERR(reset_gpio))
 		return dev_err_probe(dev, PTR_ERR(reset_gpio),
 				     "Cannot get reset GPIO\n");
 
+	powerdown_gpio = devm_gpiod_get_optional(dev, "powerdown",
+						 GPIOD_OUT_HIGH);
+	if (IS_ERR(powerdown_gpio))
+		return dev_err_probe(dev, PTR_ERR(powerdown_gpio),
+				     "Cannot get powerdown GPIO\n");
+
 	priv->reg_avdd = devm_regulator_get(dev, "avdd");
 	if (IS_ERR(priv->reg_avdd))
 		return dev_err_probe(dev, PTR_ERR(priv->reg_avdd),
@@ -863,6 +947,10 @@ static int ads1298_probe(struct spi_device *spi)
 	if (ret)
 		return ret;
 
+	ret = devm_regulator_get_enable_optional(dev, "dvdd");
+	if (ret && ret != -ENODEV)
+		return dev_err_probe(dev, ret, "Failed to enable dvdd regulator\n");
+
 	/* VREF can be supplied externally, otherwise use internal reference */
 	priv->reg_vref = devm_regulator_get_optional(dev, "vref");
 	if (IS_ERR(priv->reg_vref)) {
@@ -904,6 +992,9 @@ static int ads1298_probe(struct spi_device *spi)
 	indio_dev->channels = ads1298_channels;
 	indio_dev->info = &ads1298_info;
 
+	/* Out of power-down, now that the supplies and the clock are up */
+	gpiod_set_value_cansleep(powerdown_gpio, 0);
+
 	/* Power-on reset time, counted from when the clock is valid */
 	msleep(DIV_ROUND_UP(ADS1298_TPOR_CLOCKS * MILLI, clk_rate));
 
@@ -957,12 +1048,14 @@ static int ads1298_probe(struct spi_device *spi)
 
 static const struct spi_device_id ads1298_id[] = {
 	{ .name = "ads1298", .driver_data = (kernel_ulong_t)&ads1298_chip_info },
+	{ .name = "ads1299", .driver_data = (kernel_ulong_t)&ads1299_chip_info },
 	{ }
 };
 MODULE_DEVICE_TABLE(spi, ads1298_id);
 
 static const struct of_device_id ads1298_of_table[] = {
 	{ .compatible = "ti,ads1298", .data = &ads1298_chip_info },
+	{ .compatible = "ti,ads1299", .data = &ads1299_chip_info },
 	{ }
 };
 MODULE_DEVICE_TABLE(of, ads1298_of_table);
@@ -978,5 +1071,6 @@ static struct spi_driver ads1298_driver = {
 module_spi_driver(ads1298_driver);
 
 MODULE_AUTHOR("Mike Looijmans <mike.looijmans@topic.nl>");
-MODULE_DESCRIPTION("TI ADS1298 ADC");
+MODULE_AUTHOR("Stephan Costa Barros <stephanbrrs8@gmail.com>");
+MODULE_DESCRIPTION("TI ADS1298 and ADS1299 ADC");
 MODULE_LICENSE("GPL");
-- 
2.43.0