thermal: jc42: add JEDEC JC-42.4/TSE2004av SPD

It is designed as a generic UCLASS_THERMAL driver for any JEDEC
JC-42.4 family of on-DIMM temperature sensors (TSE2004av and
compatible parts).

The driver reads the temperature register over DM I2C.

The "jedec,jc-42.4-temp" compatible is Linux-aligned (see
Documentation/devicetree/bindings/hwmon/jedec,jc-42.4-temp.yaml in
the Linux tree).

When CMD_TEMPERATURE is enabled, the sensor becomes available with
the standard commands "temperature list" / "temperature get".

Signed-off-by: Vincent Jardin <[email protected]>
Signed-off-by: Peng Fan <[email protected]>

3 files changed, 101 insertions, 0 deletions

diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
index 91c39aa4dee..04cf3bfa420 100644
--- a/drivers/thermal/Kconfig
+++ b/drivers/thermal/Kconfig
@@ -55,4 +55,11 @@ config TI_LM74_THERMAL
 	 Enable thermal support for the Texas Instruments LM74 chip.
 	 The driver supports reading CPU temperature.
 
+config DM_THERMAL_JC42
+	bool "JEDEC JC-42.4/TSE2004av SPD temperature sensor"
+	depends on DM_I2C
+	help
+	  Enable support for the JEDEC JC-42.4 temperature sensor found
+	  on the SPD bus of DDR3 and DDR4 DIMMs (TSE2004av and compatible).
+
 endif # if DM_THERMAL
diff --git a/drivers/thermal/Makefile b/drivers/thermal/Makefile
index b6f06c00ed9..c9fa7561b45 100644
--- a/drivers/thermal/Makefile
+++ b/drivers/thermal/Makefile
@@ -11,3 +11,4 @@ obj-$(CONFIG_RCAR_GEN3_THERMAL) += rcar_gen3_thermal.o
 obj-$(CONFIG_SANDBOX) += thermal_sandbox.o
 obj-$(CONFIG_TI_DRA7_THERMAL) += ti-bandgap.o
 obj-$(CONFIG_TI_LM74_THERMAL) += ti-lm74.o
+obj-$(CONFIG_DM_THERMAL_JC42) += jc42.o
diff --git a/drivers/thermal/jc42.c b/drivers/thermal/jc42.c
new file mode 100644
index 00000000000..6945260e8b0
--- /dev/null
+++ b/drivers/thermal/jc42.c
@@ -0,0 +1,93 @@
+// 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,
+};