[PATCH v2 4/5] drivers: iio: adc: LTC2499 support

From: Ciprian Regus
Date: Thu Sep 01 2022 - 08:19:46 EST

The LTC2499 is a 16-channel (eight differential), 24-bit,
ADC with Easy Drive technology and a 2-wire, I2C interface.

Implement support for the LTC2499 ADC by extending the LTC2497
driver. A new chip_info struct is added to differentiate between
chip types and resolutions when reading data from the device.

Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/2499fe.pdf
Signed-off-by: Ciprian Regus <ciprian.regus@xxxxxxxxxx>
---
changes in v2:
- removed the bitfield.h and bitops.h includes, since they were not needed.
- removed a blank line.
- replaced the data buffer for the ltc2497_driverdata with a union.
- depending on frame size, i2c transfers use either 3 or 4 byte buffers, instead
of always using a __be32.
- added a comment which explains the output data format and how does sign extension.
happen.
- added the const modifier for the chip_info structs.
- renamed the chip_info struct to ltc2497_chip_info.
- renamed the chip_type enum to ltc2497_chip_type
- added probe fallback to using i2c_device_id in case OF fails.
- used BITS_TO_BYTES() instead of dividing by 8.
- used a tab instead of a space in a struct field declaration, which in v1 appeared as
if the line was deleted and added back.
- added back a trailing comma.
- rearranged variable declaration lines so that longer ones would be first.
- used pointers to a chip info struct in the i2c_device_id table, instead of enums.
drivers/iio/adc/ltc2496.c | 8 ++++-
drivers/iio/adc/ltc2497-core.c | 2 +-
drivers/iio/adc/ltc2497.c | 56 +++++++++++++++++++++++++++++++---
drivers/iio/adc/ltc2497.h | 11 +++++++
4 files changed, 70 insertions(+), 7 deletions(-)

diff --git a/drivers/iio/adc/ltc2496.c b/drivers/iio/adc/ltc2496.c
index dfb3bb5997e5..bf89d5ae19af 100644
--- a/drivers/iio/adc/ltc2496.c
+++ b/drivers/iio/adc/ltc2496.c
@@ -15,6 +15,7 @@
#include <linux/iio/driver.h>
#include <linux/module.h>
#include <linux/mod_devicetable.h>
+#include <linux/property.h>

#include "ltc2497.h"

@@ -74,6 +75,7 @@ static int ltc2496_probe(struct spi_device *spi)
spi_set_drvdata(spi, indio_dev);
st->spi = spi;
st->common_ddata.result_and_measure = ltc2496_result_and_measure;
+ st->common_ddata.chip_info = device_get_match_data(dev);

return ltc2497core_probe(dev, indio_dev);
}
@@ -85,8 +87,12 @@ static void ltc2496_remove(struct spi_device *spi)
ltc2497core_remove(indio_dev);
}

+static const struct ltc2497_chip_info ltc2496_info = {
+ .resolution = 16,
+};
+
static const struct of_device_id ltc2496_of_match[] = {
- { .compatible = "lltc,ltc2496", },
+ { .compatible = "lltc,ltc2496", .data = &ltc2496_info, },
{},
};
MODULE_DEVICE_TABLE(of, ltc2496_of_match);
diff --git a/drivers/iio/adc/ltc2497-core.c b/drivers/iio/adc/ltc2497-core.c
index 2a485c8a1940..b2752399402c 100644
--- a/drivers/iio/adc/ltc2497-core.c
+++ b/drivers/iio/adc/ltc2497-core.c
@@ -95,7 +95,7 @@ static int ltc2497core_read_raw(struct iio_dev *indio_dev,
return ret;

*val = ret / 1000;
- *val2 = 17;
+ *val2 = ddata->chip_info->resolution + 1;

return IIO_VAL_FRACTIONAL_LOG2;

diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c
index f7c786f37ceb..2f660015f34b 100644
--- a/drivers/iio/adc/ltc2497.c
+++ b/drivers/iio/adc/ltc2497.c
@@ -12,6 +12,7 @@
#include <linux/iio/driver.h>
#include <linux/module.h>
#include <linux/mod_devicetable.h>
+#include <linux/property.h>

#include "ltc2497.h"

@@ -19,11 +20,16 @@ struct ltc2497_driverdata {
/* this must be the first member */
struct ltc2497core_driverdata common_ddata;
struct i2c_client *client;
+ u32 recv_size;
+ u32 sub_lsb;
/*
* DMA (thus cache coherency maintenance) may require the
* transfer buffers to live in their own cache lines.
*/
- __be32 buf __aligned(IIO_DMA_MINALIGN);
+ union {
+ __be32 d32;
+ u8 d8[3];
+ } data __aligned(IIO_DMA_MINALIGN);
};

static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata,
@@ -34,13 +40,29 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata,
int ret;

if (val) {
- ret = i2c_master_recv(st->client, (char *)&st->buf, 3);
+ if (st->recv_size == 3)
+ ret = i2c_master_recv(st->client, (char *)&st->data.d8, st->recv_size);
+ else
+ ret = i2c_master_recv(st->client, (char *)&st->data.d32, st->recv_size);
+
if (ret < 0) {
dev_err(&st->client->dev, "i2c_master_recv failed\n");
return ret;
}

- *val = (be32_to_cpu(st->buf) >> 14) - (1 << 17);
+ /*
+ * The data format is 16/24 bit 2s complement, but with an upper sign bit on the
+ * resolution + 1 position, which is set for positive values only. Given this
+ * bit's value, subtracting BIT(resolution + 1) from the ADC's result is
+ * equivalent to a sign extension.
+ */
+ if (st->recv_size == 3) {
+ *val = (get_unaligned_be24(st->data.d8) >> st->sub_lsb)
+ - BIT(ddata->chip_info->resolution + 1);
+ } else {
+ *val = (be32_to_cpu(st->data.d32) >> st->sub_lsb)
+ - BIT(ddata->chip_info->resolution + 1);
+ }
}

ret = i2c_smbus_write_byte(st->client,
@@ -54,9 +76,11 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata,
static int ltc2497_probe(struct i2c_client *client,
const struct i2c_device_id *id)
{
+ const struct ltc2497_chip_info *chip_info;
struct iio_dev *indio_dev;
struct ltc2497_driverdata *st;
struct device *dev = &client->dev;
+ u32 resolution;

if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C |
I2C_FUNC_SMBUS_WRITE_BYTE))
@@ -71,6 +95,15 @@ static int ltc2497_probe(struct i2c_client *client,
st->client = client;
st->common_ddata.result_and_measure = ltc2497_result_and_measure;

+ chip_info = device_get_match_data(dev);
+ if (!chip_info)
+ chip_info = (const struct ltc2497_chip_info *)id->driver_data;
+ st->common_ddata.chip_info = chip_info;
+
+ resolution = chip_info->resolution;
+ st->sub_lsb = 31 - (resolution + 1);
+ st->recv_size = BITS_TO_BYTES(resolution) + 1;
+
return ltc2497core_probe(dev, indio_dev);
}

@@ -83,14 +116,27 @@ static int ltc2497_remove(struct i2c_client *client)
return 0;
}

+static const struct ltc2497_chip_info ltc2497_info[] = {
+ [TYPE_LTC2497] = {
+ .resolution = 16,
+ .name = NULL,
+ },
+ [TYPE_LTC2499] = {
+ .resolution = 24,
+ .name = "ltc2499",
+ },
+};
+
static const struct i2c_device_id ltc2497_id[] = {
- { "ltc2497", 0 },
+ { "ltc2497", (kernel_ulong_t)&ltc2497_info[TYPE_LTC2497] },
+ { "ltc2499", (kernel_ulong_t)&ltc2497_info[TYPE_LTC2497] },
{ }
};
MODULE_DEVICE_TABLE(i2c, ltc2497_id);

static const struct of_device_id ltc2497_of_match[] = {
- { .compatible = "lltc,ltc2497", },
+ { .compatible = "lltc,ltc2497", .data = &ltc2497_info[TYPE_LTC2497] },
+ { .compatible = "lltc,ltc2499", .data = &ltc2497_info[TYPE_LTC2499] },
{},
};
MODULE_DEVICE_TABLE(of, ltc2497_of_match);
diff --git a/drivers/iio/adc/ltc2497.h b/drivers/iio/adc/ltc2497.h
index d0b42dd6b8ad..95f6a5f4d4a6 100644
--- a/drivers/iio/adc/ltc2497.h
+++ b/drivers/iio/adc/ltc2497.h
@@ -4,9 +4,20 @@
#define LTC2497_CONFIG_DEFAULT LTC2497_ENABLE
#define LTC2497_CONVERSION_TIME_MS 150ULL

+enum ltc2497_chip_type {
+ TYPE_LTC2496,
+ TYPE_LTC2497,
+ TYPE_LTC2499,
+};
+
+struct ltc2497_chip_info {
+ u32 resolution;
+};
+
struct ltc2497core_driverdata {
struct regulator *ref;
ktime_t time_prev;
+ const struct ltc2497_chip_info *chip_info;
u8 addr_prev;
int (*result_and_measure)(struct ltc2497core_driverdata *ddata,
u8 address, int *val);
--
2.30.2