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// SPDX-License-Identifier: GPL-2.0+
/*
* Copyright 2026 Free Mobile - Vincent Jardin
*
* JEDEC JC-42.4 / TSE2004av Temperature Sensor driver.
*
* Generic I2C temperature sensor of the Serial Presence Detect (SPD)
* bus of DDR3 and DDR4 SO-DIMMs / UDIMMs / RDIMMs per the JEDEC
* JC-42.4 standard. The TSE2004av variant adds an integrated SPD
* EEPROM, but the thermal register interface is the same and is
* what this driver exposes.
*
* Register layout (subset):
* 0x05 Ambient temperature, 16-bit big-endian:
* bit 15 : T_CRIT alarm flag (read-only)
* bit 14 : T_HIGH alarm flag (read-only)
* bit 13 : T_LOW alarm flag (read-only)
* bit 12 : sign (two's-complement within bits[12:0])
* bits[11:0]: magnitude * 16 (LSB = 0.0625 degC = 62.5 mC)
* 0x06 Manufacturer ID (16-bit BE, JEP-106 vendor code)
* 0x07 Device ID + Revision (upper byte = ID, lower = revision)
* ...
*/
#include <dm.h>
#include <i2c.h>
#include <thermal.h>
#include <linux/bitops.h>
#define JC42_REG_TEMP 0x05
#define JC42_TEMP_SIGN BIT(12)
#define JC42_TEMP_MAGNITUDE GENMASK(11, 0)
static int jc42_get_temp(struct udevice *dev, int *temp)
{
u8 buf[2];
int ret;
int mag;
ret = dm_i2c_read(dev, JC42_REG_TEMP, buf, sizeof(buf));
if (ret)
return ret;
mag = ((buf[0] << 8) | buf[1]) & (JC42_TEMP_SIGN | JC42_TEMP_MAGNITUDE);
if (mag & JC42_TEMP_SIGN)
mag -= (JC42_TEMP_SIGN << 1);
/*
* mag is in units of 1/16 degC. Multiply first to keep one
* extra bit of precision before the divide. Worst-case range
* for a 13-bit signed value is +/-4096, so the product fits
* comfortably in an int (~4.1M mC).
*/
*temp = mag * 1000 / 16;
return 0;
}
static const struct dm_thermal_ops jc42_ops = {
.get_temp = jc42_get_temp,
};
/*
* Optional DT label property override: it replace the default DM
* device name (the ofnode name, eg "temp@18") so
* temperature list or temperature get commands
* show a human-meaningful identifier such as "ddr-top" or
* "ddr-bottom".
* It mirrors the Linux hwmon binding which uses label for the
* per-sensor display name.
*/
static int jc42_bind(struct udevice *dev)
{
const char *label = dev_read_string(dev, "label");
if (label && *label)
return device_set_name(dev, label);
return 0;
}
static const struct udevice_id jc42_match[] = {
{ .compatible = "jedec,jc-42.4-temp" },
{ }
};
U_BOOT_DRIVER(jc42_thermal) = {
.name = "jc42_thermal",
.id = UCLASS_THERMAL,
.of_match = jc42_match,
.bind = jc42_bind,
.ops = &jc42_ops,
};
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