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Wed, 5 Aug 2026 05:44:24 -0400 From: Andrei Stancovici To: =?UTF-8?q?Nuno=20S=C3=A1?= , Michael Hennerich , Jonathan Cameron , "David Lechner" , Andy Shevchenko , "Rob Herring" , Krzysztof Kozlowski , "Conor Dooley" , Liam Beguin , , , , CC: Andrei Stancovici Subject: [PATCH 2/3] iio: adc: ltc2497: add LTC2499 internal temperature channel Date: Wed, 5 Aug 2026 12:41:28 +0300 Message-ID: <20260805094135.11762-3-andrei.stancovici@analog.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260805094135.11762-1-andrei.stancovici@analog.com> References: <20260805094135.11762-1-andrei.stancovici@analog.com> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-ADIRuleOP-NewSCL: Rule Triggered X-Proofpoint-GUID: 0XySsyFRMezSeQ1mXzQu3mgNylNLIjMd X-Proofpoint-Spam-Info: AW1haW4tMjYwODA1MDA3NyBTYWx0ZWRfX1Mt6fmhXt1s7 DkWlgfolEdTqtTPcuPBBxgC0hb1PfihrbaAnyljf376ZDN29Mh9SLFQLqvXDtZOtwu9rV/Xmz4V lJgOMwaPgFwINdNKCV28flP4cE3g11sBFugG2KHQbbH4v+5UnSVc X-Authority-Analysis: v=2.4 cv=aY9RWxot c=1 sm=1 tr=0 ts=6a7305fd cx=c_pps a=3WNzaoukacrqR9RwcOSAdA==:117 a=3WNzaoukacrqR9RwcOSAdA==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=0sLvza09kfJOxVLZPwjg:22 a=N--XFCr6TIEc_64PeIT2:22 a=gAnH3GRIAAAA:8 a=zsLNtPQ2y0leb1ljye4A:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: 0XySsyFRMezSeQ1mXzQu3mgNylNLIjMd X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODA1MDA3NyBTYWx0ZWRfXzf8fUc0XQXcG FhhdKlk5ZYi0F9aB+g3oJ4efzj5RjUWw7SenfIjZSSCtBiu7Q0miNate2A51QPPN2yL8hks+xGV C8TNHJytVO8tTmYvMpl29qg4RJxgSGzIPpBb/kFfbV6jRFZc/5v0lPMmBjvmLOnzg5AGvameNVV r9KlFjhrHdXHeAGSKlZmZSxVrKHieEcJR+aGWx2inHjXoKT6w1VCJ9zBCJ58+Po1yc32ZNWANL9 ctnRFRlWbubnhy4F0PS9IN9r0+eVyvF8be8tMoMsTPBgNlxBZsz/tc4bPznBOYXvMn72lEES2FG 2o8O3BFc1VoXBn7jHbM5APS1At8Oktrt/4K/Aj76o3jknEwPXQfoeQpI0GPYI34Aahp1qSuLAmk jeMaf99DYmbR+IbIv3KdeAypdN3FKqZP0fd9ZcDJTPKqhsOYsBQilg+QjMmuQ2k+BO096bcWVf0 hDJccYPK/5+xn3vPtqg== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-05_03,2026-08-04_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 bulkscore=0 impostorscore=0 spamscore=0 suspectscore=0 lowpriorityscore=0 phishscore=0 clxscore=1015 adultscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608050077 The LTC2499 has an internal PTAT (proportional to absolute temperature) sensor that is activated by a second I2C configuration byte (EN2 | IM). Expose it as an IIO_TEMP channel providing raw, scale and offset so the standard IIO formula T[m°C] = (raw + offset) * scale reconstructs the temperature. The PTAT sensor yields the absolute temperature as T(K) = DATAOUT24 * Vref / 1570 (Vref in volts) The raw value exported here is sign-extended and normalised to 2^(resolution + 1) == 2^25, i.e. raw = 2 * DATAOUT24, so on the IIO milli-degree-Celsius convention scale[m°C/LSB] = Vref_uV / 3140000 offset = -273150 * 3140000 / Vref_uV The scale and offset are derived from the reference voltage returned by regulator_get_voltage(); its error is propagated as before, so a board that fails to describe vref-supply gets a clear read error instead of a silently wrong temperature. No board-specific reference value is assumed in the driver. The single temperature channel is appended as the last entry of the shared channel array and excluded via num_channels for parts without an internal sensor, so the existing LTC2497 channel layout and device name are unchanged. The LTC2499 latches its converter configuration from the second command byte and only re-evaluates it when that byte has EN2 set. EN2 | IM selects the internal temperature sensor. Because a single-byte command, or a second byte with EN2 = 0, means "keep previous", a one-byte channel select cannot pull the device back out of temperature mode: after a temperature read every subsequent voltage read would keep returning the PTAT result instead of the selected input. Temperature support is therefore only correct if the voltage path also emits a second command byte that re-selects an external input. Send two-byte commands for all conversions on parts that have the sensor (has_temp): temperature: EN2 | IM voltage: EN2 (IM = 0 -> external input) The LTC2497 and LTC2496, which lack the second-byte mechanism, keep using the original single-byte channel select and are unchanged. Signed-off-by: Andrei Stancovici --- drivers/iio/adc/ltc2497-core.c | 54 +++++++++++++++++++++++++++++++--- drivers/iio/adc/ltc2497.c | 31 +++++++++++++++++++ drivers/iio/adc/ltc2497.h | 12 ++++++++ 3 files changed, 93 insertions(+), 4 deletions(-) diff --git a/drivers/iio/adc/ltc2497-core.c b/drivers/iio/adc/ltc2497-core.c index 2dc5c7044269..4ca7271ca007 100644 --- a/drivers/iio/adc/ltc2497-core.c +++ b/drivers/iio/adc/ltc2497-core.c @@ -9,6 +9,7 @@ #include #include #include +#include #include #include #include @@ -95,10 +96,43 @@ static int ltc2497core_read_raw(struct iio_dev *indio_dev, if (ret < 0) return ret; - *val = ret / 1000; - *val2 = ddata->chip_info->resolution + 1; - - return IIO_VAL_FRACTIONAL_LOG2; + switch (chan->type) { + case IIO_TEMP: + /* + * raw is normalised to 2^(resolution + 1), i.e. + * raw = 2 * DATAOUT24, so the PTAT scale (datasheet + * Vref / 1570 per kelvin) doubles its denominator and, + * in m°C, becomes Vref_uV / 3140000. + */ + *val = ret; + *val2 = 3140000; + return IIO_VAL_FRACTIONAL; + case IIO_VOLTAGE: + *val = ret / 1000; + *val2 = ddata->chip_info->resolution + 1; + return IIO_VAL_FRACTIONAL_LOG2; + default: + return -EINVAL; + } + + case IIO_CHAN_INFO_OFFSET: + switch (chan->type) { + case IIO_TEMP: + ret = regulator_get_voltage(ddata->ref); + if (ret < 0) + return ret; + /* + * 0 °C == 273.15 K must map to raw + offset such that + * (raw + offset) * scale == 0 m°C, i.e. + * offset = -273150 / scale + * = -273150 * 3140000 / Vref_uV + * Computed in 64-bit to avoid overflow. + */ + *val = div_s64(-273150LL * 3140000, ret); + return IIO_VAL_INT; + default: + return -EINVAL; + } default: return -EINVAL; @@ -126,6 +160,14 @@ static int ltc2497core_read_raw(struct iio_dev *indio_dev, .differential = 1, \ } +#define LTC2497_TEMP_CHANNEL { \ + .type = IIO_TEMP, \ + .address = LTC2497_TEMP_ADDR, \ + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | \ + 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 +201,7 @@ static const struct iio_chan_spec ltc2497core_channel[] = { 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_TEMP_CHANNEL, }; static const struct iio_info ltc2497core_info = { @@ -184,6 +227,9 @@ int ltc2497core_probe(struct device *dev, struct iio_dev *indio_dev) indio_dev->modes = INDIO_DIRECT_MODE; indio_dev->channels = ltc2497core_channel; indio_dev->num_channels = ARRAY_SIZE(ltc2497core_channel); + /* Only the ltc2499 has a temperature channel; it is the last entry. */ + if (!ddata->chip_info->has_temp) + indio_dev->num_channels--; 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 c1668b5a351e..2ff53b292f74 100644 --- a/drivers/iio/adc/ltc2497.c +++ b/drivers/iio/adc/ltc2497.c @@ -84,6 +84,36 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata, return 0; } + /* + * Parts with the internal PTAT sensor (LTC2499) latch their converter + * configuration via a second command byte and only re-evaluate it when + * that byte has EN2 set; a single byte, or a second byte with EN2 = 0, + * means "keep previous". A one-byte channel select therefore cannot pull + * the device back out of temperature mode, so a voltage read after a + * temperature read would keep returning the PTAT result. Always drive the + * second byte with EN2 set on these parts: IM | temperature-rejection for + * a temperature read, EN2 alone (IM = 0) to (re)select an external input. + */ + if (ddata->chip_info->has_temp) { + u8 cmd[2]; + + if (address == LTC2497_TEMP_ADDR) { + cmd[0] = LTC2497_ENABLE | LTC2497_CONFIG_DEFAULT; + cmd[1] = LTC2499_EN2 | LTC2499_IM; + } else { + cmd[0] = LTC2497_ENABLE | address; + cmd[1] = LTC2499_EN2; + } + + ret = i2c_master_send(st->client, cmd, sizeof(cmd)); + if (ret < 0) { + dev_err(&st->client->dev, "i2c transfer failed: %pe\n", + ERR_PTR(ret)); + return ret; + } + return 0; + } + ret = i2c_smbus_write_byte(st->client, LTC2497_ENABLE | address); if (ret) @@ -137,6 +167,7 @@ static const struct ltc2497_chip_info ltc2497_info[] = { [TYPE_LTC2499] = { .resolution = 24, .name = "ltc2499", + .has_temp = true, }, }; diff --git a/drivers/iio/adc/ltc2497.h b/drivers/iio/adc/ltc2497.h index 64e81c95a3dd..1da2cfec3b6a 100644 --- a/drivers/iio/adc/ltc2497.h +++ b/drivers/iio/adc/ltc2497.h @@ -4,9 +4,21 @@ #define LTC2497_CONFIG_DEFAULT LTC2497_ENABLE #define LTC2497_CONVERSION_TIME_MS 150ULL +/* + * Sentinel passed as `address` to result_and_measure() to request a + * temperature conversion instead of a voltage channel. Valid channel + * addresses fit in 5 bits (0x00–0x1F), so 0xFF is unambiguous. + */ +#define LTC2497_TEMP_ADDR 0xFF + +/* Second config-byte bits (LTC2499 / LTC2493 only) */ +#define LTC2499_EN2 BIT(7) /* enable second config byte */ +#define LTC2499_IM BIT(6) /* 1 = measure internal temp sensor */ + struct ltc2497_chip_info { u32 resolution; const char *name; + bool has_temp; }; struct ltc2497core_driverdata { -- 2.43.0