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Message-Id: <20250813-ltc2495-v2-3-bbaf20f6ba07@gmail.com>
Date: Wed, 13 Aug 2025 18:54:31 +0200
From: Yusuf Alper Bilgin <y.alperbilgin@...il.com>
To: Lars-Peter Clausen <lars@...afoo.de>,
Michael Hennerich <Michael.Hennerich@...log.com>,
Jonathan Cameron <jic23@...nel.org>, David Lechner <dlechner@...libre.com>,
Nuno Sá <nuno.sa@...log.com>,
Andy Shevchenko <andy@...nel.org>, Rob Herring <robh@...nel.org>,
Krzysztof Kozlowski <krzk+dt@...nel.org>,
Conor Dooley <conor+dt@...nel.org>, Liam Beguin <liambeguin@...il.com>
Cc: Michael Hennerich <michael.hennerich@...log.com>,
linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org, Yusuf Alper Bilgin <y.alperbilgin@...il.com>
Subject: [PATCH v2 3/4] iio: adc: ltc2497: add temperature sensor support
Support for reading the internal temperature sensor on LTC2495 and
LTC2499 via a standard IIO temperature channel.
Signed-off-by: Yusuf Alper Bilgin <y.alperbilgin@...il.com>
---
drivers/iio/adc/ltc2497-core.c | 140 ++++++++++++++++++++++++++++++-----------
drivers/iio/adc/ltc2497.c | 28 ++++++++-
drivers/iio/adc/ltc2497.h | 17 ++++-
3 files changed, 145 insertions(+), 40 deletions(-)
diff --git a/drivers/iio/adc/ltc2497-core.c b/drivers/iio/adc/ltc2497-core.c
index 2dc5c704426949a4ec62c42591d6c2c40ffb79cc..0e21d5f59e6108be8b5d79bd706425278043b44d 100644
--- a/drivers/iio/adc/ltc2497-core.c
+++ b/drivers/iio/adc/ltc2497-core.c
@@ -18,6 +18,7 @@
#define LTC2497_SGL BIT(4)
#define LTC2497_DIFF 0
#define LTC2497_SIGN BIT(3)
+#define LTC2497_KELVIN_TO_CELCIUS 273
static int ltc2497core_wait_conv(struct ltc2497core_driverdata *ddata)
{
@@ -95,10 +96,53 @@ static int ltc2497core_read_raw(struct iio_dev *indio_dev,
if (ret < 0)
return ret;
- *val = ret / 1000;
- *val2 = ddata->chip_info->resolution + 1;
+ switch (chan->type) {
+ case IIO_VOLTAGE:
+ *val = ret / 1000;
+ *val2 = ddata->chip_info->resolution + 1;
+
+ return IIO_VAL_FRACTIONAL_LOG2;
+
+ case IIO_TEMP:
+ if (!ddata->chip_info->has_temp_channel)
+ return -EINVAL;
+
+ /*
+ * The datasheet formula to get Temperature in Celsius is:
+ * Temp_C = (DATAOUT * Vref_V / temp_scale) - 273
+ *
+ * To match the IIO framework's model of (raw + offset) * scale,
+ * and to get the final result in millidegrees Celsius:
+ *
+ * Temp_mC = ((DATAOUT * Vref_mV / temp_scale_mV) - 273) * 1000
+ * Temp_mC = (DATAOUT - (273 * temp_scale_mV / Vref_mv)) * 1000 *
+ * Vref_mV / temp_scale_mV
+ *
+ * This gives us:
+ * scale = Vref_mV * 1000 / temp_scale_mV
+ * offset = -273 * temp_scale / Vref_mV
+ */
+ *val = ret;
+ *val2 = ddata->chip_info->temp_scale_mV;
+
+ return IIO_VAL_FRACTIONAL;
+
+ default:
+ return -EINVAL;
+ }
+ case IIO_CHAN_INFO_OFFSET:
+ if (chan->type != IIO_TEMP)
+ return -EINVAL;
+
+ /* see the calculation above. Offset with (-273 * temp_scale / Vref) */
+ ret = regulator_get_voltage(ddata->ref);
+ if (ret < 0)
+ return ret;
- return IIO_VAL_FRACTIONAL_LOG2;
+ *val = -LTC2497_KELVIN_TO_CELCIUS * ddata->chip_info->temp_scale_mV;
+ *val2 = ret / 1000;
+
+ return IIO_VAL_FRACTIONAL;
default:
return -EINVAL;
@@ -126,39 +170,55 @@ static int ltc2497core_read_raw(struct iio_dev *indio_dev,
.differential = 1, \
}
+#define LTC2497_T_CHAN { \
+ .type = IIO_TEMP, \
+ .channel = 0, \
+ .address = (LTC2497_ENABLE_TEMPERATURE_CONV), \
+ .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), \
+ .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET), \
+}
+
+#define LTC2497_CHANNELS \
+ LTC2497_CHAN(0, LTC2497_SGL, "CH0"), \
+ LTC2497_CHAN(1, LTC2497_SGL, "CH1"), \
+ LTC2497_CHAN(2, LTC2497_SGL, "CH2"), \
+ LTC2497_CHAN(3, LTC2497_SGL, "CH3"), \
+ LTC2497_CHAN(4, LTC2497_SGL, "CH4"), \
+ LTC2497_CHAN(5, LTC2497_SGL, "CH5"), \
+ LTC2497_CHAN(6, LTC2497_SGL, "CH6"), \
+ LTC2497_CHAN(7, LTC2497_SGL, "CH7"), \
+ LTC2497_CHAN(8, LTC2497_SGL, "CH8"), \
+ LTC2497_CHAN(9, LTC2497_SGL, "CH9"), \
+ LTC2497_CHAN(10, LTC2497_SGL, "CH10"), \
+ LTC2497_CHAN(11, LTC2497_SGL, "CH11"), \
+ LTC2497_CHAN(12, LTC2497_SGL, "CH12"), \
+ LTC2497_CHAN(13, LTC2497_SGL, "CH13"), \
+ LTC2497_CHAN(14, LTC2497_SGL, "CH14"), \
+ LTC2497_CHAN(15, LTC2497_SGL, "CH15"), \
+ LTC2497_CHAN_DIFF(0, LTC2497_DIFF), \
+ LTC2497_CHAN_DIFF(1, LTC2497_DIFF), \
+ LTC2497_CHAN_DIFF(2, LTC2497_DIFF), \
+ LTC2497_CHAN_DIFF(3, LTC2497_DIFF), \
+ LTC2497_CHAN_DIFF(4, LTC2497_DIFF), \
+ LTC2497_CHAN_DIFF(5, LTC2497_DIFF), \
+ LTC2497_CHAN_DIFF(6, LTC2497_DIFF), \
+ LTC2497_CHAN_DIFF(7, LTC2497_DIFF), \
+ LTC2497_CHAN_DIFF(0, LTC2497_DIFF | LTC2497_SIGN), \
+ LTC2497_CHAN_DIFF(1, LTC2497_DIFF | LTC2497_SIGN), \
+ LTC2497_CHAN_DIFF(2, LTC2497_DIFF | LTC2497_SIGN), \
+ LTC2497_CHAN_DIFF(3, LTC2497_DIFF | LTC2497_SIGN), \
+ LTC2497_CHAN_DIFF(4, LTC2497_DIFF | LTC2497_SIGN), \
+ LTC2497_CHAN_DIFF(5, LTC2497_DIFF | LTC2497_SIGN), \
+ LTC2497_CHAN_DIFF(6, LTC2497_DIFF | LTC2497_SIGN), \
+ LTC2497_CHAN_DIFF(7, LTC2497_DIFF | LTC2497_SIGN)
+
static const struct iio_chan_spec ltc2497core_channel[] = {
- LTC2497_CHAN(0, LTC2497_SGL, "CH0"),
- LTC2497_CHAN(1, LTC2497_SGL, "CH1"),
- LTC2497_CHAN(2, LTC2497_SGL, "CH2"),
- LTC2497_CHAN(3, LTC2497_SGL, "CH3"),
- LTC2497_CHAN(4, LTC2497_SGL, "CH4"),
- LTC2497_CHAN(5, LTC2497_SGL, "CH5"),
- LTC2497_CHAN(6, LTC2497_SGL, "CH6"),
- LTC2497_CHAN(7, LTC2497_SGL, "CH7"),
- LTC2497_CHAN(8, LTC2497_SGL, "CH8"),
- LTC2497_CHAN(9, LTC2497_SGL, "CH9"),
- LTC2497_CHAN(10, LTC2497_SGL, "CH10"),
- LTC2497_CHAN(11, LTC2497_SGL, "CH11"),
- LTC2497_CHAN(12, LTC2497_SGL, "CH12"),
- LTC2497_CHAN(13, LTC2497_SGL, "CH13"),
- LTC2497_CHAN(14, LTC2497_SGL, "CH14"),
- LTC2497_CHAN(15, LTC2497_SGL, "CH15"),
- LTC2497_CHAN_DIFF(0, LTC2497_DIFF),
- LTC2497_CHAN_DIFF(1, LTC2497_DIFF),
- LTC2497_CHAN_DIFF(2, LTC2497_DIFF),
- LTC2497_CHAN_DIFF(3, LTC2497_DIFF),
- LTC2497_CHAN_DIFF(4, LTC2497_DIFF),
- LTC2497_CHAN_DIFF(5, LTC2497_DIFF),
- LTC2497_CHAN_DIFF(6, LTC2497_DIFF),
- LTC2497_CHAN_DIFF(7, LTC2497_DIFF),
- LTC2497_CHAN_DIFF(0, LTC2497_DIFF | LTC2497_SIGN),
- LTC2497_CHAN_DIFF(1, LTC2497_DIFF | LTC2497_SIGN),
- LTC2497_CHAN_DIFF(2, LTC2497_DIFF | LTC2497_SIGN),
- LTC2497_CHAN_DIFF(3, LTC2497_DIFF | LTC2497_SIGN),
- LTC2497_CHAN_DIFF(4, LTC2497_DIFF | LTC2497_SIGN),
- LTC2497_CHAN_DIFF(5, LTC2497_DIFF | LTC2497_SIGN),
- LTC2497_CHAN_DIFF(6, LTC2497_DIFF | LTC2497_SIGN),
- LTC2497_CHAN_DIFF(7, LTC2497_DIFF | LTC2497_SIGN),
+ LTC2497_CHANNELS,
+};
+
+static const struct iio_chan_spec ltc2497core_channel_with_temperature[] = {
+ LTC2497_CHANNELS,
+ LTC2497_T_CHAN,
};
static const struct iio_info ltc2497core_info = {
@@ -182,8 +242,14 @@ int ltc2497core_probe(struct device *dev, struct iio_dev *indio_dev)
indio_dev->info = <c2497core_info;
indio_dev->modes = INDIO_DIRECT_MODE;
- indio_dev->channels = ltc2497core_channel;
- indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel);
+
+ if (ddata->chip_info->has_temp_channel) {
+ indio_dev->channels = ltc2497core_channel_with_temperature;
+ indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel_with_temperature);
+ } else {
+ indio_dev->channels = ltc2497core_channel;
+ indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel);
+ }
ret = ddata->result_and_measure(ddata, LTC2497_CONFIG_DEFAULT, NULL);
if (ret < 0)
diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c
index 8f4665547b5b0d32084599f8557c40102c37a4ce..07fced79aeead3778964b114d479fdcb643c16df 100644
--- a/drivers/iio/adc/ltc2497.c
+++ b/drivers/iio/adc/ltc2497.c
@@ -86,8 +86,28 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata,
return 0;
}
- ret = i2c_smbus_write_byte(st->client,
- LTC2497_ENABLE | address);
+ /*
+ * Chips with temperature sensor support (e.g., LTC2495/LTC2499)
+ * require a two-byte command format to select any channel.
+ *
+ * To read the internal temperature, LTC2497_ENABLE_TEMPERATURE_CONV
+ * is sent as the second byte. To read a voltage channel, LTC2497_EN2
+ * is sent, which sets the default configuration: simultaneous 50/60Hz
+ * rejection, 1x speed, and gain=1.
+ *
+ * Chips without this feature use a standard single-byte command.
+ */
+ if (ddata->chip_info->has_temp_channel) {
+ if (address == LTC2497_ENABLE_TEMPERATURE_CONV)
+ ret = i2c_smbus_write_byte_data(st->client, LTC2497_ENABLE,
+ LTC2497_ENABLE_TEMPERATURE_CONV);
+ else
+ ret = i2c_smbus_write_byte_data(st->client, LTC2497_ENABLE | address,
+ LTC2497_EN2);
+ } else {
+ ret = i2c_smbus_write_byte(st->client, LTC2497_ENABLE | address);
+ }
+
if (ret)
dev_err(&st->client->dev, "i2c transfer failed: %pe\n",
ERR_PTR(ret));
@@ -135,6 +155,8 @@ static const struct ltc2497_chip_info ltc2497_info[] = {
[TYPE_LTC2495] = {
.resolution = 16,
.name = "ltc2495",
+ .has_temp_channel = true,
+ .temp_scale_mV = 12250,
},
[TYPE_LTC2497] = {
.resolution = 16,
@@ -143,6 +165,8 @@ static const struct ltc2497_chip_info ltc2497_info[] = {
[TYPE_LTC2499] = {
.resolution = 24,
.name = "ltc2499",
+ .has_temp_channel = true,
+ .temp_scale_mV = 1570000,
},
};
diff --git a/drivers/iio/adc/ltc2497.h b/drivers/iio/adc/ltc2497.h
index 64e81c95a3dd05911b6717c09ac0560c9f47f304..7f53bf8b8469d2371bb7ae64ce90a61beadba9ba 100644
--- a/drivers/iio/adc/ltc2497.h
+++ b/drivers/iio/adc/ltc2497.h
@@ -3,10 +3,25 @@
#define LTC2497_ENABLE 0xA0
#define LTC2497_CONFIG_DEFAULT LTC2497_ENABLE
#define LTC2497_CONVERSION_TIME_MS 150ULL
+#define LTC2497_EN2 BIT(7)
+/* Enable the internal temperature sensor */
+#define LTC2497_IM BIT(6)
+/* Second command byte value to initiate a temperature conversion */
+#define LTC2497_ENABLE_TEMPERATURE_CONV (LTC2497_EN2 | LTC2497_IM)
struct ltc2497_chip_info {
- u32 resolution;
const char *name;
+ u32 resolution;
+ /*
+ * Represents the datasheet constant from the temperature formula:
+ * T_Kelvin = (DATAOUT * Vref) / temp_scale, where Vref is in Volts.
+ *
+ * To allow the driver to use Vref in millivolts for the calculation
+ * and also to avoid floating points, this stored value represents the
+ * datasheet constant scaled by 1000.
+ */
+ u32 temp_scale_mV;
+ bool has_temp_channel;
};
struct ltc2497core_driverdata {
--
2.43.0
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