diff mbox series

[v4,2/2] iio: adc: ti-ads1298: Add driver

Message ID 20240214063736.88283-2-mike.looijmans@topic.nl (mailing list archive)
State Changes Requested
Headers show
Series [v4,1/2] dt-bindings: iio: adc: ti-ads1298: Add bindings | expand

Commit Message

Mike Looijmans Feb. 14, 2024, 6:37 a.m. UTC
Skeleton driver for the TI ADS1298 medical ADC. This device is
typically used for ECG and similar measurements. Supports data
acquisition at configurable scale and sampling frequency.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>

---

Changes in v4:
Explain rdata_xfer_busy better and remove post-decrement
Reset assert explanation and add cansleep
Additional style changes

Changes in v3:
Indentation fixups
Remove unused headers
Remove #define leftovers
Use devm_get_clk_optional_enabled
Use ilog2 instead of fls()-1
Magic "23" replaced
Explain the extra "0" in read/write register
use guard() from cleanup.h
use REGCACHE_MAPLE

Changes in v2:
Remove accidental "default y" in Kconfig
Indentation and similar cosmetic fixes
Magic numbers into constants
Short return paths in read_raw and write_raw
DMA buffer alignment
Bounce buffer is u32 instead of u8
Avoid races using claim_direct_mode
Check errors on all register accesses
Immediate SPI restart to reduce underruns
"name" is chip name, not unique

 drivers/iio/adc/Kconfig      |  11 +
 drivers/iio/adc/Makefile     |   1 +
 drivers/iio/adc/ti-ads1298.c | 766 +++++++++++++++++++++++++++++++++++
 3 files changed, 778 insertions(+)
 create mode 100644 drivers/iio/adc/ti-ads1298.c

Comments

Jonathan Cameron Feb. 16, 2024, 1:38 p.m. UTC | #1
On Wed, 14 Feb 2024 07:37:36 +0100
Mike Looijmans <mike.looijmans@topic.nl> wrote:

> Skeleton driver for the TI ADS1298 medical ADC. This device is
> typically used for ECG and similar measurements. Supports data
> acquisition at configurable scale and sampling frequency.
> 
> Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
> 
Hi Mike,

One final thing noticed on a (hopefully) last read through.

/sys/bus/iio:device0/name is going to read ads1298 whichever
chip is detected.

Would be more useful to users if it identified the actual
part given that is easily read from the ID register.

Jonathan

> ---
> 
> Changes in v4:
> Explain rdata_xfer_busy better and remove post-decrement
> Reset assert explanation and add cansleep
> Additional style changes
> 
> Changes in v3:
> Indentation fixups
> Remove unused headers
> Remove #define leftovers
> Use devm_get_clk_optional_enabled
> Use ilog2 instead of fls()-1
> Magic "23" replaced
> Explain the extra "0" in read/write register
> use guard() from cleanup.h
> use REGCACHE_MAPLE
> 
> Changes in v2:
> Remove accidental "default y" in Kconfig
> Indentation and similar cosmetic fixes
> Magic numbers into constants
> Short return paths in read_raw and write_raw
> DMA buffer alignment
> Bounce buffer is u32 instead of u8
> Avoid races using claim_direct_mode
> Check errors on all register accesses
> Immediate SPI restart to reduce underruns
> "name" is chip name, not unique

I missed this until having a final read through but it's not the chip name
in the driver currently - the name is always ads1298 despite there being a handy
ID register that tells us what we actually have.


> 
>  drivers/iio/adc/Kconfig      |  11 +
>  drivers/iio/adc/Makefile     |   1 +
>  drivers/iio/adc/ti-ads1298.c | 766 +++++++++++++++++++++++++++++++++++
>  3 files changed, 778 insertions(+)
>  create mode 100644 drivers/iio/adc/ti-ads1298.c

> +
> +static const char *ads1298_family_name(unsigned int id)
> +{
> +	switch (id & ADS1298_MASK_ID_FAMILY) {
> +	case ADS1298_ID_FAMILY_ADS129X:
> +		return "ADS129x";
> +	case ADS1298_ID_FAMILY_ADS129XR:
> +		return "ADS129xR";
> +	default:
> +		return "(unknown)";
> +	}
> +}

...

> +static int ads1298_probe(struct spi_device *spi)
> +{

...

> +
> +	priv->tx_buffer[0] = ADS1298_CMD_RDATA;
> +	priv->rdata_xfer.tx_buf = priv->tx_buffer;
> +	priv->rdata_xfer.rx_buf = priv->rx_buffer;
> +	priv->rdata_xfer.len = ADS1298_SPI_RDATA_BUFFER_SIZE;
> +	/* Must keep CS low for 4 clocks */
> +	priv->rdata_xfer.delay.value = 2;
> +	priv->rdata_xfer.delay.unit = SPI_DELAY_UNIT_USECS;
> +	spi_message_init_with_transfers(&priv->rdata_msg, &priv->rdata_xfer, 1);
> +	priv->rdata_msg.complete = &ads1298_rdata_complete;
> +	priv->rdata_msg.context = indio_dev;
> +
> +	indio_dev->name = spi_get_device_id(spi)->name;

I was going to just tweak this whilst applying.  Using the spi device id often
ends up being fragile in the long term because of the split between the different
ID tables and the mess that happens if fallback compatibles are in use and
the spi IDs are missing (you will get a warning about this at runtime
but it'll carry on anyway).

Easier to just hard code the name for now and when you have multiple
devices supported, add this to a chip_info type structure.
Or we could make it support the more specific name given the detection above.
Is there a reason to not do that given a more accurate name is
easy to work out and may be useful to a user?

Jonathan
Mike Looijmans Feb. 16, 2024, 2:01 p.m. UTC | #2
On 16-02-2024 14:38, Jonathan Cameron wrote:
> On Wed, 14 Feb 2024 07:37:36 +0100
> Mike Looijmans <mike.looijmans@topic.nl> wrote:
>
>> Skeleton driver for the TI ADS1298 medical ADC. This device is
>> typically used for ECG and similar measurements. Supports data
>> acquisition at configurable scale and sampling frequency.
>>
>> Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
>>
> Hi Mike,
>
> One final thing noticed on a (hopefully) last read through.
>
> /sys/bus/iio:device0/name is going to read ads1298 whichever
> chip is detected.
>
> Would be more useful to users if it identified the actual
> part given that is easily read from the ID register.

Makes sense. So It would say "ads1296" or "ads1298r" for example. I 
guess we prefer all lower-case here.


>
> Jonathan
>
>> ---
>>
>> Changes in v4:
>> Explain rdata_xfer_busy better and remove post-decrement
>> Reset assert explanation and add cansleep
>> Additional style changes
>>
>> Changes in v3:
>> Indentation fixups
>> Remove unused headers
>> Remove #define leftovers
>> Use devm_get_clk_optional_enabled
>> Use ilog2 instead of fls()-1
>> Magic "23" replaced
>> Explain the extra "0" in read/write register
>> use guard() from cleanup.h
>> use REGCACHE_MAPLE
>>
>> Changes in v2:
>> Remove accidental "default y" in Kconfig
>> Indentation and similar cosmetic fixes
>> Magic numbers into constants
>> Short return paths in read_raw and write_raw
>> DMA buffer alignment
>> Bounce buffer is u32 instead of u8
>> Avoid races using claim_direct_mode
>> Check errors on all register accesses
>> Immediate SPI restart to reduce underruns
>> "name" is chip name, not unique
> I missed this until having a final read through but it's not the chip name
> in the driver currently - the name is always ads1298 despite there being a handy
> ID register that tells us what we actually have.
>
>
>>   drivers/iio/adc/Kconfig      |  11 +
>>   drivers/iio/adc/Makefile     |   1 +
>>   drivers/iio/adc/ti-ads1298.c | 766 +++++++++++++++++++++++++++++++++++
>>   3 files changed, 778 insertions(+)
>>   create mode 100644 drivers/iio/adc/ti-ads1298.c
>> +
>> +static const char *ads1298_family_name(unsigned int id)
>> +{
>> +	switch (id & ADS1298_MASK_ID_FAMILY) {
>> +	case ADS1298_ID_FAMILY_ADS129X:
>> +		return "ADS129x";
>> +	case ADS1298_ID_FAMILY_ADS129XR:
>> +		return "ADS129xR";
>> +	default:
>> +		return "(unknown)";
>> +	}
>> +}
> ...
>
>> +static int ads1298_probe(struct spi_device *spi)
>> +{
> ...
>
>> +
>> +	priv->tx_buffer[0] = ADS1298_CMD_RDATA;
>> +	priv->rdata_xfer.tx_buf = priv->tx_buffer;
>> +	priv->rdata_xfer.rx_buf = priv->rx_buffer;
>> +	priv->rdata_xfer.len = ADS1298_SPI_RDATA_BUFFER_SIZE;
>> +	/* Must keep CS low for 4 clocks */
>> +	priv->rdata_xfer.delay.value = 2;
>> +	priv->rdata_xfer.delay.unit = SPI_DELAY_UNIT_USECS;
>> +	spi_message_init_with_transfers(&priv->rdata_msg, &priv->rdata_xfer, 1);
>> +	priv->rdata_msg.complete = &ads1298_rdata_complete;
>> +	priv->rdata_msg.context = indio_dev;
>> +
>> +	indio_dev->name = spi_get_device_id(spi)->name;
> I was going to just tweak this whilst applying.  Using the spi device id often
> ends up being fragile in the long term because of the split between the different
> ID tables and the mess that happens if fallback compatibles are in use and
> the spi IDs are missing (you will get a warning about this at runtime
> but it'll carry on anyway).
>
> Easier to just hard code the name for now and when you have multiple
> devices supported, add this to a chip_info type structure.
> Or we could make it support the more specific name given the detection above.
> Is there a reason to not do that given a more accurate name is
> easy to work out and may be useful to a user?
>
The only reason I tried to make the "name" unique is that IIO 
oscilloscope (ab)uses "name" as a unique identifier. That's something 
that ought to be fixed in IIO oscilloscope.

Giving the chip name would reveal the actual detected hardware, there's 
currently no other way for the user to find that out.
Mike Looijmans Feb. 16, 2024, 3:04 p.m. UTC | #3
On 16-02-2024 14:38, Jonathan Cameron wrote:
> On Wed, 14 Feb 2024 07:37:36 +0100
> Mike Looijmans <mike.looijmans@topic.nl> wrote:
>
>> Skeleton driver for the TI ADS1298 medical ADC. This device is
>> typically used for ECG and similar measurements. Supports data
>> acquisition at configurable scale and sampling frequency.
>>
>> Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
>>
> Hi Mike,
>
> One final thing noticed on a (hopefully) last read through.
>
> /sys/bus/iio:device0/name is going to read ads1298 whichever
> chip is detected.
>
> Would be more useful to users if it identified the actual
> part given that is easily read from the ID register.

Implemented it like that, the "name" now reflects the chip's information.

While at it, I also made the probe fail on invalid ID (tested by probing 
an empty SPI bus)

And also pass the channel count into the "num_channels" member, and 
adapted the SPI transaction, which should support the devices with 4 or 
6 channels better.

I'll post a v5 soon, bit of testing first...
diff mbox series

Patch

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 35f9867da12c..1d2d2eff15da 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -1318,6 +1318,17 @@  config TI_ADS8688
 	  This driver can also be built as a module. If so, the module will be
 	  called ti-ads8688.
 
+config TI_ADS1298
+	tristate "Texas Instruments ADS1298"
+	depends on SPI
+	select IIO_BUFFER
+	help
+	  If you say yes here you get support for Texas Instruments ADS1298
+	  medical ADC chips
+
+	  This driver can also be built as a module. If so, the module will be
+	  called ti-ads1298.
+
 config TI_ADS124S08
 	tristate "Texas Instruments ADS124S08"
 	depends on SPI
diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
index bee11d442af4..ff0e3633eded 100644
--- a/drivers/iio/adc/Makefile
+++ b/drivers/iio/adc/Makefile
@@ -117,6 +117,7 @@  obj-$(CONFIG_TI_ADS7924) += ti-ads7924.o
 obj-$(CONFIG_TI_ADS7950) += ti-ads7950.o
 obj-$(CONFIG_TI_ADS8344) += ti-ads8344.o
 obj-$(CONFIG_TI_ADS8688) += ti-ads8688.o
+obj-$(CONFIG_TI_ADS1298) += ti-ads1298.o
 obj-$(CONFIG_TI_ADS124S08) += ti-ads124s08.o
 obj-$(CONFIG_TI_ADS131E08) += ti-ads131e08.o
 obj-$(CONFIG_TI_AM335X_ADC) += ti_am335x_adc.o
diff --git a/drivers/iio/adc/ti-ads1298.c b/drivers/iio/adc/ti-ads1298.c
new file mode 100644
index 000000000000..ab2ab2116f52
--- /dev/null
+++ b/drivers/iio/adc/ti-ads1298.c
@@ -0,0 +1,766 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/* TI ADS1298 chip family driver
+ * Copyright (C) 2023 - 2024 Topic Embedded Products
+ */
+
+#include <linux/bitfield.h>
+#include <linux/cleanup.h>
+#include <linux/clk.h>
+#include <linux/err.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/gpio/consumer.h>
+#include <linux/log2.h>
+#include <linux/math.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/regulator/consumer.h>
+#include <linux/slab.h>
+#include <linux/spi/spi.h>
+#include <linux/units.h>
+
+#include <linux/iio/iio.h>
+#include <linux/iio/buffer.h>
+#include <linux/iio/kfifo_buf.h>
+
+#include <asm/unaligned.h>
+
+/* Commands */
+#define ADS1298_CMD_WAKEUP	0x02
+#define ADS1298_CMD_STANDBY	0x04
+#define ADS1298_CMD_RESET	0x06
+#define ADS1298_CMD_START	0x08
+#define ADS1298_CMD_STOP	0x0a
+#define ADS1298_CMD_RDATAC	0x10
+#define ADS1298_CMD_SDATAC	0x11
+#define ADS1298_CMD_RDATA	0x12
+#define ADS1298_CMD_RREG	0x20
+#define ADS1298_CMD_WREG	0x40
+
+/* Registers */
+#define ADS1298_REG_ID		0x00
+#define ADS1298_MASK_ID_FAMILY			GENMASK(7, 3)
+#define ADS1298_MASK_ID_CHANNELS		GENMASK(2, 0)
+#define ADS1298_ID_FAMILY_ADS129X		0x90
+#define ADS1298_ID_FAMILY_ADS129XR		0xd0
+
+#define ADS1298_REG_CONFIG1	0x01
+#define ADS1298_MASK_CONFIG1_HR			BIT(7)
+#define ADS1298_MASK_CONFIG1_DR			GENMASK(2, 0)
+#define ADS1298_SHIFT_DR_HR			6
+#define ADS1298_SHIFT_DR_LP			7
+#define ADS1298_LOWEST_DR			0x06
+
+#define ADS1298_REG_CONFIG2	0x02
+#define ADS1298_MASK_CONFIG2_RESERVED		BIT(6)
+#define ADS1298_MASK_CONFIG2_WCT_CHOP		BIT(5)
+#define ADS1298_MASK_CONFIG2_INT_TEST		BIT(4)
+#define ADS1298_MASK_CONFIG2_TEST_AMP		BIT(2)
+#define ADS1298_MASK_CONFIG2_TEST_FREQ_DC	GENMASK(1, 0)
+#define ADS1298_MASK_CONFIG2_TEST_FREQ_SLOW	0
+#define ADS1298_MASK_CONFIG2_TEST_FREQ_FAST	BIT(0)
+
+#define ADS1298_REG_CONFIG3	0x03
+#define ADS1298_MASK_CONFIG3_PWR_REFBUF		BIT(7)
+#define ADS1298_MASK_CONFIG3_RESERVED		BIT(6)
+#define ADS1298_MASK_CONFIG3_VREF_4V		BIT(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_REG_LOFF_STATP	0x12
+#define ADS1298_REG_LOFF_STATN	0x13
+#define ADS1298_REG_CONFIG4	0x17
+#define ADS1298_MASK_CONFIG4_SINGLE_SHOT	BIT(3)
+
+#define ADS1298_REG_WCT1	0x18
+#define ADS1298_REG_WCT2	0x19
+
+#define ADS1298_MAX_CHANNELS	8
+#define ADS1298_BITS_PER_SAMPLE	24
+#define ADS1298_CLK_RATE_HZ	2048000
+#define ADS1298_CLOCKS_TO_USECS(x) \
+		(DIV_ROUND_UP((x) * MICROHZ_PER_HZ, ADS1298_CLK_RATE_HZ))
+/*
+ * Read/write register commands require 4 clocks to decode, for speeds above
+ * 2x the clock rate, this would require extra time between the command byte and
+ * the data. Much simpler is to just limit the SPI transfer speed while doing
+ * register access.
+ */
+#define ADS1298_SPI_BUS_SPEED_SLOW	ADS1298_CLK_RATE_HZ
+/* For reading and writing registers, we need a 3-byte buffer */
+#define ADS1298_SPI_CMD_BUFFER_SIZE	3
+/* Outputs status word and 8 24-bit samples, plus the command byte */
+#define ADS1298_SPI_RDATA_BUFFER_SIZE	((ADS1298_MAX_CHANNELS + 1) * 3 + 1)
+
+struct ads1298_private {
+	const struct ads1298_chip_info *chip_info;
+	struct spi_device *spi;
+	struct regulator *reg_avdd;
+	struct regulator *reg_vref;
+	struct clk *clk;
+	struct regmap *regmap;
+	struct completion completion;
+	struct iio_trigger *trig;
+	struct spi_transfer rdata_xfer;
+	struct spi_message rdata_msg;
+	spinlock_t irq_busy_lock; /* Handshake between SPI and DRDY irqs */
+	/*
+	 * rdata_xfer_busy increments when a DRDY occurs and decrements when SPI
+	 * completion is reported. Hence its meaning is:
+	 * 0 = Waiting for DRDY interrupt
+	 * 1 = SPI transfer in progress
+	 * 2 = DRDY during SPI transfer, start another transfer on completion
+	 * >2 = Multiple DRDY during transfer, lost rdata_xfer_busy - 2 samples
+	 */
+	unsigned int rdata_xfer_busy;
+
+	/* Temporary storage for demuxing data after SPI transfer */
+	u32 bounce_buffer[ADS1298_MAX_CHANNELS];
+
+	/* For synchronous SPI exchanges (read/write registers) */
+	u8 cmd_buffer[ADS1298_SPI_CMD_BUFFER_SIZE] __aligned(IIO_DMA_MINALIGN);
+
+	/* Buffer used for incoming SPI data */
+	u8 rx_buffer[ADS1298_SPI_RDATA_BUFFER_SIZE];
+	/* Contains the RDATA command and zeroes to clock out */
+	u8 tx_buffer[ADS1298_SPI_RDATA_BUFFER_SIZE];
+};
+
+/* Three bytes per sample in RX buffer, starting at offset 4 */
+#define ADS1298_OFFSET_IN_RX_BUFFER(index)	(3 * (index) + 4)
+
+#define ADS1298_CHAN(index)				\
+{							\
+	.type = IIO_VOLTAGE,				\
+	.indexed = 1,					\
+	.channel = index,				\
+	.address = ADS1298_OFFSET_IN_RX_BUFFER(index),	\
+	.info_mask_separate =				\
+		BIT(IIO_CHAN_INFO_RAW) |		\
+		BIT(IIO_CHAN_INFO_SCALE),		\
+	.info_mask_shared_by_all =			\
+		BIT(IIO_CHAN_INFO_SAMP_FREQ) |		\
+		BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),	\
+	.scan_index = index,				\
+	.scan_type = {					\
+		.sign = 's',				\
+		.realbits = ADS1298_BITS_PER_SAMPLE,	\
+		.storagebits = 32,			\
+		.endianness = IIO_CPU,			\
+	},						\
+}
+
+static const struct iio_chan_spec ads1298_channels[] = {
+	ADS1298_CHAN(0),
+	ADS1298_CHAN(1),
+	ADS1298_CHAN(2),
+	ADS1298_CHAN(3),
+	ADS1298_CHAN(4),
+	ADS1298_CHAN(5),
+	ADS1298_CHAN(6),
+	ADS1298_CHAN(7),
+};
+
+static int ads1298_write_cmd(struct ads1298_private *priv, u8 command)
+{
+	struct spi_transfer xfer = {
+		.tx_buf = priv->cmd_buffer,
+		.rx_buf = priv->cmd_buffer,
+		.len = 1,
+		.speed_hz = ADS1298_SPI_BUS_SPEED_SLOW,
+		.delay = {
+			.value = 2,
+			.unit = SPI_DELAY_UNIT_USECS,
+		},
+	};
+
+	priv->cmd_buffer[0] = command;
+
+	return spi_sync_transfer(priv->spi, &xfer, 1);
+}
+
+static int ads1298_read_one(struct ads1298_private *priv, int chan_index)
+{
+	int ret;
+
+	/* Enable the channel */
+	ret = regmap_update_bits(priv->regmap, ADS1298_REG_CHnSET(chan_index),
+				 ADS1298_MASK_CH_PD, 0);
+	if (ret)
+		return ret;
+
+	/* Enable single-shot mode, so we don't need to send a STOP */
+	ret = regmap_update_bits(priv->regmap, ADS1298_REG_CONFIG4,
+				 ADS1298_MASK_CONFIG4_SINGLE_SHOT,
+				 ADS1298_MASK_CONFIG4_SINGLE_SHOT);
+	if (ret)
+		return ret;
+
+	reinit_completion(&priv->completion);
+
+	ret = ads1298_write_cmd(priv, ADS1298_CMD_START);
+	if (ret < 0) {
+		dev_err(&priv->spi->dev, "CMD_START error: %d\n", ret);
+		return ret;
+	}
+
+	/* Cannot take longer than 40ms (250Hz) */
+	ret = wait_for_completion_timeout(&priv->completion, msecs_to_jiffies(50));
+	if (!ret)
+		return -ETIMEDOUT;
+
+	return 0;
+}
+
+static int ads1298_get_samp_freq(struct ads1298_private *priv, int *val)
+{
+	unsigned long rate;
+	unsigned int cfg;
+	int ret;
+
+	ret = regmap_read(priv->regmap, ADS1298_REG_CONFIG1, &cfg);
+	if (ret)
+		return ret;
+
+	if (priv->clk)
+		rate = clk_get_rate(priv->clk);
+	else
+		rate = ADS1298_CLK_RATE_HZ;
+	if (!rate)
+		return -EINVAL;
+
+	/* Data rate shift depends on HR/LP mode */
+	if (cfg & ADS1298_MASK_CONFIG1_HR)
+		rate >>= ADS1298_SHIFT_DR_HR;
+	else
+		rate >>= ADS1298_SHIFT_DR_LP;
+
+	*val = rate >> (cfg & ADS1298_MASK_CONFIG1_DR);
+
+	return IIO_VAL_INT;
+}
+
+static int ads1298_set_samp_freq(struct ads1298_private *priv, int val)
+{
+	unsigned long rate;
+	unsigned int factor;
+	unsigned int cfg;
+
+	if (priv->clk)
+		rate = clk_get_rate(priv->clk);
+	else
+		rate = ADS1298_CLK_RATE_HZ;
+	if (!rate)
+		return -EINVAL;
+
+	factor = (rate >> ADS1298_SHIFT_DR_HR) / val;
+	if (factor >= BIT(ADS1298_SHIFT_DR_LP))
+		cfg = ADS1298_LOWEST_DR;
+	else if (factor)
+		cfg = ADS1298_MASK_CONFIG1_HR | ilog2(factor); /* Use HR mode */
+	else
+		cfg = ADS1298_MASK_CONFIG1_HR; /* Fastest possible */
+
+	return regmap_update_bits(priv->regmap, ADS1298_REG_CONFIG1,
+				  ADS1298_MASK_CONFIG1_HR | ADS1298_MASK_CONFIG1_DR,
+				  cfg);
+}
+
+static const u8 ads1298_pga_settings[] = { 6, 1, 2, 3, 4, 8, 12 };
+
+static int ads1298_get_scale(struct ads1298_private *priv,
+			     int channel, int *val, int *val2)
+{
+	int ret;
+	unsigned int regval;
+	u8 gain;
+
+	if (priv->reg_vref) {
+		ret = regulator_get_voltage(priv->reg_vref);
+		if (ret < 0)
+			return ret;
+
+		*val = ret / MILLI; /* Convert to millivolts */
+	} else {
+		ret = regmap_read(priv->regmap, ADS1298_REG_CONFIG3, &regval);
+		if (ret)
+			return ret;
+
+		/* Refererence in millivolts */
+		*val = regval & ADS1298_MASK_CONFIG3_VREF_4V ? 4000 : 2400;
+	}
+
+	ret = regmap_read(priv->regmap, ADS1298_REG_CHnSET(channel), &regval);
+	if (ret)
+		return ret;
+
+	gain = ads1298_pga_settings[FIELD_GET(ADS1298_MASK_CH_PGA, regval)];
+	*val /= gain; /* Full scale is VREF / gain */
+
+	*val2 = ADS1298_BITS_PER_SAMPLE - 1; /* Signed, hence the -1 */
+
+	return IIO_VAL_FRACTIONAL_LOG2;
+}
+
+static int ads1298_read_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan,
+			    int *val, int *val2, long mask)
+{
+	struct ads1298_private *priv = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = iio_device_claim_direct_mode(indio_dev);
+		if (ret)
+			return ret;
+
+		ret = ads1298_read_one(priv, chan->scan_index);
+
+		iio_device_release_direct_mode(indio_dev);
+
+		if (ret)
+			return ret;
+
+		*val = sign_extend32(get_unaligned_be24(priv->rx_buffer + chan->address),
+				     ADS1298_BITS_PER_SAMPLE - 1);
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		return ads1298_get_scale(priv, chan->channel, val, val2);
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		return ads1298_get_samp_freq(priv, val);
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		ret = regmap_read(priv->regmap, ADS1298_REG_CONFIG1, val);
+		if (ret)
+			return ret;
+
+		*val = 16 << (*val & ADS1298_MASK_CONFIG1_DR);
+		return IIO_VAL_INT;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int ads1298_write_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan, int val,
+			     int val2, long mask)
+{
+	struct ads1298_private *priv = iio_priv(indio_dev);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		return ads1298_set_samp_freq(priv, val);
+	default:
+		return -EINVAL;
+	}
+}
+
+static int ads1298_reg_write(void *context, unsigned int reg, unsigned int val)
+{
+	struct ads1298_private *priv = context;
+	struct spi_transfer reg_write_xfer = {
+		.tx_buf = priv->cmd_buffer,
+		.rx_buf = priv->cmd_buffer,
+		.len = 3,
+		.speed_hz = ADS1298_SPI_BUS_SPEED_SLOW,
+		.delay = {
+			.value = 2,
+			.unit = SPI_DELAY_UNIT_USECS,
+		},
+	};
+
+	priv->cmd_buffer[0] = ADS1298_CMD_WREG | reg;
+	priv->cmd_buffer[1] = 0; /* Number of registers to be written - 1 */
+	priv->cmd_buffer[2] = val;
+
+	return spi_sync_transfer(priv->spi, &reg_write_xfer, 1);
+}
+
+static int ads1298_reg_read(void *context, unsigned int reg, unsigned int *val)
+{
+	struct ads1298_private *priv = context;
+	struct spi_transfer reg_read_xfer = {
+		.tx_buf = priv->cmd_buffer,
+		.rx_buf = priv->cmd_buffer,
+		.len = 3,
+		.speed_hz = ADS1298_SPI_BUS_SPEED_SLOW,
+		.delay = {
+			.value = 2,
+			.unit = SPI_DELAY_UNIT_USECS,
+		},
+	};
+	int ret;
+
+	priv->cmd_buffer[0] = ADS1298_CMD_RREG | reg;
+	priv->cmd_buffer[1] = 0; /* Number of registers to be read - 1 */
+	priv->cmd_buffer[2] = 0;
+
+	ret = spi_sync_transfer(priv->spi, &reg_read_xfer, 1);
+	if (ret)
+		return ret;
+
+	*val = priv->cmd_buffer[2];
+
+	return 0;
+}
+
+static int ads1298_reg_access(struct iio_dev *indio_dev, unsigned int reg,
+			      unsigned int writeval, unsigned int *readval)
+{
+	struct ads1298_private *priv = iio_priv(indio_dev);
+
+	if (readval)
+		return regmap_read(priv->regmap, reg, readval);
+
+	return regmap_write(priv->regmap, reg, writeval);
+}
+
+static void ads1298_rdata_unmark_busy(struct ads1298_private *priv)
+{
+	/* Notify we're no longer waiting for the SPI transfer to complete */
+	guard(spinlock_irqsave)(&priv->irq_busy_lock);
+	priv->rdata_xfer_busy = 0;
+}
+
+static int ads1298_update_scan_mode(struct iio_dev *indio_dev,
+				    const unsigned long *scan_mask)
+{
+	struct ads1298_private *priv = iio_priv(indio_dev);
+	unsigned int val;
+	int ret;
+	int i;
+
+	/* Make the interrupt routines start with a clean slate */
+	ads1298_rdata_unmark_busy(priv);
+
+	/* Configure power-down bits to match scan mask */
+	for (i = 0; i < ADS1298_MAX_CHANNELS; i++) {
+		val = test_bit(i, scan_mask) ? 0 : ADS1298_MASK_CH_PD;
+		ret = regmap_update_bits(priv->regmap, ADS1298_REG_CHnSET(i),
+					 ADS1298_MASK_CH_PD, val);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static const struct iio_info ads1298_info = {
+	.read_raw = &ads1298_read_raw,
+	.write_raw = &ads1298_write_raw,
+	.update_scan_mode = &ads1298_update_scan_mode,
+	.debugfs_reg_access = &ads1298_reg_access,
+};
+
+static void ads1298_rdata_release_busy_or_restart(struct ads1298_private *priv)
+{
+	guard(spinlock_irqsave)(&priv->irq_busy_lock);
+
+	if (priv->rdata_xfer_busy > 1) {
+		/*
+		 * DRDY interrupt occurred before SPI completion. Start a new
+		 * SPI transaction now to retrieve the data that wasn't latched
+		 * into the ADS1298 chip's transfer buffer yet.
+		 */
+		spi_async(priv->spi, &priv->rdata_msg);
+		/*
+		 * If more than one DRDY took place, there was an overrun. Since
+		 * the sample is already lost, reset the counter to 1 so that
+		 * we will wait for a DRDY interrupt after this SPI transaction.
+		 */
+		priv->rdata_xfer_busy = 1;
+	} else {
+		/* No pending data, wait for DRDY */
+		priv->rdata_xfer_busy = 0;
+	}
+}
+
+/* Called from SPI completion interrupt handler */
+static void ads1298_rdata_complete(void *context)
+{
+	struct iio_dev *indio_dev = context;
+	struct ads1298_private *priv = iio_priv(indio_dev);
+	int scan_index;
+	u32 *bounce = priv->bounce_buffer;
+
+	if (!iio_buffer_enabled(indio_dev)) {
+		/*
+		 * for a single transfer mode we're kept in direct_mode until
+		 * completion, avoiding a race with buffered IO.
+		 */
+		ads1298_rdata_unmark_busy(priv);
+		complete(&priv->completion);
+		return;
+	}
+
+	/* Demux the channel data into our bounce buffer */
+	for_each_set_bit(scan_index, indio_dev->active_scan_mask,
+			 indio_dev->masklength) {
+		const struct iio_chan_spec *scan_chan =
+					&indio_dev->channels[scan_index];
+		const u8 *data = priv->rx_buffer + scan_chan->address;
+
+		*bounce++ = get_unaligned_be24(data);
+	}
+
+	/* rx_buffer can be overwritten from this point on */
+	ads1298_rdata_release_busy_or_restart(priv);
+
+	iio_push_to_buffers(indio_dev, priv->bounce_buffer);
+}
+
+static irqreturn_t ads1298_interrupt(int irq, void *dev_id)
+{
+	struct iio_dev *indio_dev = dev_id;
+	struct ads1298_private *priv = iio_priv(indio_dev);
+	unsigned int wasbusy;
+
+	guard(spinlock_irqsave)(&priv->irq_busy_lock);
+
+	wasbusy = priv->rdata_xfer_busy++;
+	/* When no SPI transfer in transit, start one now */
+	if (!wasbusy)
+		spi_async(priv->spi, &priv->rdata_msg);
+
+	return IRQ_HANDLED;
+};
+
+static int ads1298_buffer_postenable(struct iio_dev *indio_dev)
+{
+	struct ads1298_private *priv = iio_priv(indio_dev);
+	int ret;
+
+	/* Disable single-shot mode */
+	ret = regmap_update_bits(priv->regmap, ADS1298_REG_CONFIG4,
+				 ADS1298_MASK_CONFIG4_SINGLE_SHOT, 0);
+	if (ret)
+		return ret;
+
+	return ads1298_write_cmd(priv, ADS1298_CMD_START);
+}
+
+static int ads1298_buffer_predisable(struct iio_dev *indio_dev)
+{
+	struct ads1298_private *priv = iio_priv(indio_dev);
+
+	return ads1298_write_cmd(priv, ADS1298_CMD_STOP);
+}
+
+static const struct iio_buffer_setup_ops ads1298_setup_ops = {
+	.postenable = &ads1298_buffer_postenable,
+	.predisable = &ads1298_buffer_predisable,
+};
+
+static void ads1298_reg_disable(void *reg)
+{
+	regulator_disable(reg);
+}
+
+static const struct regmap_range ads1298_regmap_volatile_range[] = {
+	regmap_reg_range(ADS1298_REG_LOFF_STATP, ADS1298_REG_LOFF_STATN),
+};
+
+static const struct regmap_access_table ads1298_regmap_volatile = {
+	.yes_ranges = ads1298_regmap_volatile_range,
+	.n_yes_ranges = ARRAY_SIZE(ads1298_regmap_volatile_range),
+};
+
+static const struct regmap_config ads1298_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.reg_read = ads1298_reg_read,
+	.reg_write = ads1298_reg_write,
+	.max_register = ADS1298_REG_WCT2,
+	.volatile_table = &ads1298_regmap_volatile,
+	.cache_type = REGCACHE_MAPLE,
+};
+
+static const char *ads1298_family_name(unsigned int id)
+{
+	switch (id & ADS1298_MASK_ID_FAMILY) {
+	case ADS1298_ID_FAMILY_ADS129X:
+		return "ADS129x";
+	case ADS1298_ID_FAMILY_ADS129XR:
+		return "ADS129xR";
+	default:
+		return "(unknown)";
+	}
+}
+
+static int ads1298_init(struct ads1298_private *priv)
+{
+	struct device *dev = &priv->spi->dev;
+	int ret;
+	unsigned int val;
+
+	/* Device initializes into RDATAC mode, which we don't want */
+	ret = ads1298_write_cmd(priv, ADS1298_CMD_SDATAC);
+	if (ret)
+		return ret;
+
+	ret = regmap_read(priv->regmap, ADS1298_REG_ID, &val);
+	if (ret)
+		return ret;
+
+	dev_dbg(dev, "Found %s, %u channels\n", ads1298_family_name(val),
+		(unsigned int)(4 + 2 * (val & ADS1298_MASK_ID_CHANNELS)));
+
+	/* Enable internal test signal, double amplitude, double frequency */
+	ret = regmap_write(priv->regmap, ADS1298_REG_CONFIG2,
+			   ADS1298_MASK_CONFIG2_RESERVED |
+			   ADS1298_MASK_CONFIG2_INT_TEST |
+			   ADS1298_MASK_CONFIG2_TEST_AMP |
+			   ADS1298_MASK_CONFIG2_TEST_FREQ_FAST);
+	if (ret)
+		return ret;
+
+	val = ADS1298_MASK_CONFIG3_RESERVED; /* Must write 1 always */
+	if (!priv->reg_vref) {
+		/* Enable internal reference */
+		val |= ADS1298_MASK_CONFIG3_PWR_REFBUF;
+		/* Use 4V VREF when power supply is at least 4.4V */
+		if (regulator_get_voltage(priv->reg_avdd) >= 4400000)
+			val |= ADS1298_MASK_CONFIG3_VREF_4V;
+	}
+	return regmap_write(priv->regmap, ADS1298_REG_CONFIG3, val);
+}
+
+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 *reset_gpio;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*priv));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	priv = iio_priv(indio_dev);
+
+	/* Reset 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, ret, "Cannot get reset GPIO\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)) {
+		if (PTR_ERR(priv->reg_vref) != -ENODEV)
+			return dev_err_probe(dev, PTR_ERR(priv->reg_avdd),
+					     "Failed to get vref regulator\n");
+
+		priv->reg_vref = NULL;
+	} else {
+		ret = regulator_enable(priv->reg_vref);
+		if (ret)
+			return ret;
+
+		ret = devm_add_action_or_reset(dev, ads1298_reg_disable, priv->reg_vref);
+		if (ret)
+			return ret;
+	}
+
+	priv->clk = devm_clk_get_optional_enabled(dev, "clk");
+	if (IS_ERR(priv->clk))
+		return dev_err_probe(dev, PTR_ERR(priv->clk), "Failed to get clk\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),
+				     "Failed to get avdd regulator\n");
+
+	ret = regulator_enable(priv->reg_avdd);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to enable avdd regulator\n");
+
+	ret = devm_add_action_or_reset(dev, ads1298_reg_disable, priv->reg_avdd);
+	if (ret)
+		return ret;
+
+	priv->spi = spi;
+	init_completion(&priv->completion);
+	spin_lock_init(&priv->irq_busy_lock);
+	priv->regmap = devm_regmap_init(dev, NULL, priv, &ads1298_regmap_config);
+	if (IS_ERR(priv->regmap))
+		return PTR_ERR(priv->regmap);
+
+	priv->tx_buffer[0] = ADS1298_CMD_RDATA;
+	priv->rdata_xfer.tx_buf = priv->tx_buffer;
+	priv->rdata_xfer.rx_buf = priv->rx_buffer;
+	priv->rdata_xfer.len = ADS1298_SPI_RDATA_BUFFER_SIZE;
+	/* Must keep CS low for 4 clocks */
+	priv->rdata_xfer.delay.value = 2;
+	priv->rdata_xfer.delay.unit = SPI_DELAY_UNIT_USECS;
+	spi_message_init_with_transfers(&priv->rdata_msg, &priv->rdata_xfer, 1);
+	priv->rdata_msg.complete = &ads1298_rdata_complete;
+	priv->rdata_msg.context = indio_dev;
+
+	indio_dev->name = spi_get_device_id(spi)->name;
+	indio_dev->modes = INDIO_DIRECT_MODE | INDIO_BUFFER_SOFTWARE;
+	indio_dev->channels = ads1298_channels;
+	indio_dev->num_channels = ADS1298_MAX_CHANNELS;
+	indio_dev->info = &ads1298_info;
+
+	if (reset_gpio) {
+		/*
+		 * Deassert reset now that clock and power are active.
+		 * Minimum reset pulsewidth is 2 clock cycles.
+		 */
+		udelay(ADS1298_CLOCKS_TO_USECS(2));
+		gpiod_set_value_cansleep(reset_gpio, 0);
+	} else {
+		ret = ads1298_write_cmd(priv, ADS1298_CMD_RESET);
+		if (ret)
+			return dev_err_probe(dev, ret, "RESET failed\n");
+	}
+	/* Wait 18 clock cycles for reset command to complete */
+	udelay(ADS1298_CLOCKS_TO_USECS(18));
+
+	ret = ads1298_init(priv);
+	if (ret)
+		return dev_err_probe(dev, ret, "Init failed\n");
+
+	ret = devm_request_irq(dev, spi->irq, &ads1298_interrupt,
+			       IRQF_TRIGGER_FALLING, indio_dev->name,
+			       indio_dev);
+	if (ret)
+		return ret;
+
+	ret = devm_iio_kfifo_buffer_setup(dev, indio_dev, &ads1298_setup_ops);
+	if (ret)
+		return ret;
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+static const struct spi_device_id ads1298_id[] = {
+	{ "ads1298" },
+	{ }
+};
+MODULE_DEVICE_TABLE(spi, ads1298_id);
+
+static const struct of_device_id ads1298_of_table[] = {
+	{ .compatible = "ti,ads1298" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ads1298_of_table);
+
+static struct spi_driver ads1298_driver = {
+	.driver = {
+		.name	= "ads1298",
+		.of_match_table = ads1298_of_table,
+	},
+	.probe		= ads1298_probe,
+	.id_table	= ads1298_id,
+};
+module_spi_driver(ads1298_driver);
+
+MODULE_AUTHOR("Mike Looijmans <mike.looijmans@topic.nl>");
+MODULE_DESCRIPTION("TI ADS1298 ADC");
+MODULE_LICENSE("GPL");