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Message-Id: <20250812-ltc2495-v1-3-7bf4c6feec2e@gmail.com>
Date: Tue, 12 Aug 2025 19:04:12 +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 3/3] iio: adc: ltc2497: add temperature sensor support
The LTC2495 and LTC2499 include an internal temperature sensor. This
patch adds support for reading it via a standard IIO temperature
channel.
Signed-off-by: Yusuf Alper Bilgin <y.alperbilgin@...il.com>
---
drivers/iio/adc/ltc2496.c | 1 +
drivers/iio/adc/ltc2497-core.c | 80 ++++++++++++++++++++++++++++++++++++++----
drivers/iio/adc/ltc2497.c | 33 ++++++++++++++---
drivers/iio/adc/ltc2497.h | 7 +++-
4 files changed, 109 insertions(+), 12 deletions(-)
diff --git a/drivers/iio/adc/ltc2496.c b/drivers/iio/adc/ltc2496.c
index f06dd0b9a85819935abea6496abe2a808ac549c6..909dbd5f9aee877aafe423b47581ff4f36a76c52 100644
--- a/drivers/iio/adc/ltc2496.c
+++ b/drivers/iio/adc/ltc2496.c
@@ -90,6 +90,7 @@ static void ltc2496_remove(struct spi_device *spi)
static const struct ltc2497_chip_info ltc2496_info = {
.resolution = 16,
.name = NULL,
+ .has_temp_channel = false,
};
static const struct of_device_id ltc2496_of_match[] = {
diff --git a/drivers/iio/adc/ltc2497-core.c b/drivers/iio/adc/ltc2497-core.c
index 400f4fe5af30e8e16b75506726235f10f2a4237f..938259df4d27e9e26dea2be4112bef355adaaafb 100644
--- a/drivers/iio/adc/ltc2497-core.c
+++ b/drivers/iio/adc/ltc2497-core.c
@@ -72,8 +72,8 @@ static int ltc2497core_read(struct ltc2497core_driverdata *ddata, u8 address, in
}
static int ltc2497core_read_raw(struct iio_dev *indio_dev,
- struct iio_chan_spec const *chan,
- int *val, int *val2, long mask)
+ struct iio_chan_spec const *chan,
+ int *val, int *val2, long mask)
{
struct ltc2497core_driverdata *ddata = iio_priv(indio_dev);
int ret;
@@ -93,10 +93,52 @@ 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 = (Conversion * Vref / temp_scale) - 273
+ *
+ * To match the IIO framework's model of (raw + offset) * scale,
+ * and to get the final result in millidegrees Celsius:
+ *
+ * = ((Conversion * Vref / temp_scale) - 273) * 1000
+ * = (Conversion - (273 * temp_scale / Vref)) * 1000 * Vref / temp_scale
+ *
+ * This gives us if the Vref is in mV:
+ * scale = Vref * 1000 / temp_scale
+ * offset = -273 * temp_scale / Vref
+ */
+ *val = ret;
+ *val2 = ddata->chip_info->temp_scale;
+
+ 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 = -273 * ddata->chip_info->temp_scale;
+ *val2 = ret / 1000;
+
+ return IIO_VAL_FRACTIONAL;
default:
return -EINVAL;
@@ -124,6 +166,14 @@ static int ltc2497core_read_raw(struct iio_dev *indio_dev,
.differential = 1, \
}
+#define LTC2497_T_CHAN() { \
+ .type = IIO_TEMP, \
+ .channel = 0, \
+ .address = (LTC2497_TEMP_CMD_ADDR), \
+ .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), \
+ .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET), \
+}
+
static const struct iio_chan_spec ltc2497core_channel[] = {
LTC2497_CHAN(0, LTC2497_SGL, "CH0"),
LTC2497_CHAN(1, LTC2497_SGL, "CH1"),
@@ -159,6 +209,8 @@ static const struct iio_chan_spec ltc2497core_channel[] = {
LTC2497_CHAN_DIFF(7, LTC2497_DIFF | LTC2497_SIGN),
};
+static const struct iio_chan_spec ltc2497_temp_channel = LTC2497_T_CHAN();
+
static const struct iio_info ltc2497core_info = {
.read_raw = ltc2497core_read_raw,
};
@@ -180,8 +232,22 @@ 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);
+
+ /* Dynamically create the channel list */
+ if (ddata->chip_info->has_temp_channel) {
+ /* Allocate space for common channels + 1 temp channel */
+ indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel) + 1;
+ indio_dev->channels = devm_kmemdup(dev, ltc2497core_channel,
+ sizeof(ltc2497core_channel), GFP_KERNEL);
+ if (!indio_dev->channels)
+ return -ENOMEM;
+
+ memcpy((void *)&indio_dev->channels[ARRAY_SIZE(ltc2497core_channel)],
+ <c2497_temp_channel, sizeof(ltc2497_temp_channel));
+ } 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..3f8515ef465d3fda7572d63ef3a265dec89079ea 100644
--- a/drivers/iio/adc/ltc2497.c
+++ b/drivers/iio/adc/ltc2497.c
@@ -86,11 +86,31 @@ 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_TEMP_CMD_ADDR 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_TEMP_CMD_ADDR)
+ ret = i2c_smbus_write_byte_data(st->client, LTC2497_ENABLE,
+ LTC2497_TEMP_CMD_ADDR);
+ 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));
+ dev_err(&st->client->dev, "i2c transfer failed: %pe\n", ERR_PTR(ret));
return ret;
}
@@ -135,14 +155,19 @@ static const struct ltc2497_chip_info ltc2497_info[] = {
[TYPE_LTC2495] = {
.resolution = 16,
.name = "ltc2495",
+ .has_temp_channel = true,
+ .temp_scale = 12250, /* 12.250 V per degree C -> 12250 mV */
},
[TYPE_LTC2497] = {
.resolution = 16,
.name = NULL,
+ .has_temp_channel = false,
},
[TYPE_LTC2499] = {
.resolution = 24,
.name = "ltc2499",
+ .has_temp_channel = true,
+ .temp_scale = 1570000, /* 1570 V per degree C -> 1570000 mV */
},
};
diff --git a/drivers/iio/adc/ltc2497.h b/drivers/iio/adc/ltc2497.h
index f2139f260c3fe4e8772c6db9c46331de775dcd5c..c133a4fb8092b1c6a66a7336016dd361783f531c 100644
--- a/drivers/iio/adc/ltc2497.h
+++ b/drivers/iio/adc/ltc2497.h
@@ -1,10 +1,15 @@
/* SPDX-License-Identifier: GPL-2.0-only */
-#define LTC2497_ENABLE 0xA0
+#define LTC2497_ENABLE 0xA0
+#define LTC2497_EN2 0x80
+#define LTC2497_IM 0x40
+#define LTC2497_TEMP_CMD_ADDR (LTC2497_EN2 | LTC2497_IM)
struct ltc2497_chip_info {
u32 resolution;
const char *name;
+ bool has_temp_channel;
+ u32 temp_scale; /* in mV, for temp conversion */
};
struct ltc2497core_driverdata {
--
2.43.0
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