hwmon: (lm70) Add ti,tmp125 support

The TMP125 is a 2 degree Celsius accurate Digital
Temperature Sensor with a SPI interface.

The temperature register is a 16-bit, read-only register.
The MSB (Bit 15) is a leading zero and never set. Bits 14
to 5 are the 1+9 temperature data bits in a two's
complement format. Bits 4 to 0 are useless copies of
Bit 5 value and therefore ignored.

This was tested on a Aerohive HiveAP-350.

Bonus: lm70 supports TMP122/TMP124 as well.
I added them to the Kconfig module description.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Link: https://lore.kernel.org/r/43b19cbd4e7f51e9509e561b02b5d8d0e7079fac.1645175187.git.chunkeey@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/lm70.rst

@@ -15,6 +15,10 @@ Supported chips:
 
     Information: https://www.ti.com/product/tmp122
 
+  * Texas Instruments TMP125
+
+    Information: https://www.ti.com/product/tmp125
+
   * National Semiconductor LM71
 
     Datasheet: https://www.ti.com/product/LM71
@@ -53,6 +57,9 @@ The LM74 and TMP121/TMP122/TMP123/TMP124 are very similar; main difference is
 
 The TMP122/TMP124 also feature configurable temperature thresholds.
 
+The TMP125 is less accurate and provides 10-bit temperature data
+with 0.25 degrees Celsius resolution.
+
 The LM71 is also very similar; main difference is 14-bit temperature
 data (0.03125 degrees celsius resolution).
 

drivers/hwmon/Kconfig

@@ -1224,8 +1224,8 @@ config SENSORS_LM70
 	depends on SPI_MASTER
 	help
 	  If you say yes here you get support for the National Semiconductor
-	  LM70, LM71, LM74 and Texas Instruments TMP121/TMP123 digital tempera-
+	  LM70, LM71, LM74 and Texas Instruments TMP121/TMP123, TMP122/TMP124,
-	  ture sensor chips.
+	  TMP125 digital temperature sensor chips.
 
 	  This driver can also be built as a module. If so, the module
 	  will be called lm70.

drivers/hwmon/lm70.c

@@ -34,6 +34,7 @@
 #define LM70_CHIP_LM71		2	/* NS LM71 */
 #define LM70_CHIP_LM74		3	/* NS LM74 */
 #define LM70_CHIP_TMP122	4	/* TI TMP122/TMP124 */
+#define LM70_CHIP_TMP125	5	/* TI TMP125 */
 
 struct lm70 {
 	struct spi_device *spi;
@@ -87,6 +88,12 @@ static ssize_t temp1_input_show(struct device *dev,
 	 * LM71:
 	 * 14 bits of 2's complement data, discard LSB 2 bits,
 	 * resolution 0.0312 degrees celsius.
+	 *
+	 * TMP125:
+	 * MSB/D15 is a leading zero. D14 is the sign-bit. This is
+	 * followed by 9 temperature bits (D13..D5) in 2's complement
+	 * data format with a resolution of 0.25 degrees celsius per unit.
+	 * LSB 5 bits (D4..D0) share the same value as D5 and get discarded.
 	 */
 	switch (p_lm70->chip) {
 	case LM70_CHIP_LM70:
@@ -102,6 +109,10 @@ static ssize_t temp1_input_show(struct device *dev,
 	case LM70_CHIP_LM71:
 		val = ((int)raw / 4) * 3125 / 100;
 		break;
+
+	case LM70_CHIP_TMP125:
+		val = (sign_extend32(raw, 14) / 32) * 250;
+		break;
 	}
 
 	status = sprintf(buf, "%d\n", val); /* millidegrees Celsius */
@@ -135,6 +146,10 @@ static const struct of_device_id lm70_of_ids[] = {
 		.compatible = "ti,tmp122",
 		.data = (void *) LM70_CHIP_TMP122,
 	},
+	{
+		.compatible = "ti,tmp125",
+		.data = (void *) LM70_CHIP_TMP125,
+	},
 	{
 		.compatible = "ti,lm71",
 		.data = (void *) LM70_CHIP_LM71,
@@ -184,6 +199,7 @@ static const struct spi_device_id lm70_ids[] = {
 	{ "lm70",   LM70_CHIP_LM70 },
 	{ "tmp121", LM70_CHIP_TMP121 },
 	{ "tmp122", LM70_CHIP_TMP122 },
+	{ "tmp125", LM70_CHIP_TMP125 },
 	{ "lm71",   LM70_CHIP_LM71 },
 	{ "lm74",   LM70_CHIP_LM74 },
 	{ },