ASoC: tas2764: expose die temp to hwmon

TAS2764 contains an ADC that reports the chip's die temperature.
The temperature in degrees Celsius is yielded by subtracting 93
from the raw value reported by the ADC.

Expose the codec die temperature to the hwmon interface.

The chip will initialise the temperature register to 2.6 *C
to avoid triggering over temp protection. As the ADC is powered
down during software shutdown, this value will persist until the
chip is fully powered up (e.g. when the PCM it's attached to is
opened). When the chip is powered back down, the last value sampled
will persist in the register.

Co-developed-by: Martin Povišer <povik+lin@cutebit.org>
Signed-off-by: Martin Povišer <povik+lin@cutebit.org>
Signed-off-by: James Calligeros <jcalligeros99@gmail.com>
Link: https://patch.msgid.link/20250406-apple-codec-changes-v5-8-50a00ec850a3@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/tas2764.c

@@ -8,6 +8,7 @@
 #include <linux/err.h>
 #include <linux/init.h>
 #include <linux/delay.h>
+#include <linux/hwmon.h>
 #include <linux/pm.h>
 #include <linux/i2c.h>
 #include <linux/gpio/consumer.h>
@@ -577,6 +578,80 @@ static int tas2764_apply_init_quirks(struct tas2764_priv *tas2764)
 	return 0;
 }
 
+static int tas2764_read_die_temp(struct tas2764_priv *tas2764, long *result)
+{
+	int ret, reg;
+
+	ret = regmap_read(tas2764->regmap, TAS2764_TEMP, &reg);
+	if (ret)
+		return ret;
+	/*
+	 * As per datasheet, subtract 93 from raw value to get degrees
+	 * Celsius. hwmon wants millidegrees.
+	 *
+	 * NOTE: The chip will initialise the TAS2764_TEMP register to
+	 * 2.6 *C to avoid triggering temperature protection. Since the
+	 * ADC is powered down during software shutdown, this value will
+	 * persist until the chip is fully powered up (e.g. the PCM it's
+	 * attached to is opened). The ADC will power down again when
+	 * the chip is put back into software shutdown, with the last
+	 * value sampled persisting in the ADC's register.
+	 */
+	*result = (reg - 93) * 1000;
+	return 0;
+}
+
+static umode_t tas2764_hwmon_is_visible(const void *data,
+					enum hwmon_sensor_types type, u32 attr,
+					int channel)
+{
+	if (type != hwmon_temp)
+		return 0;
+
+	switch (attr) {
+	case hwmon_temp_input:
+		return 0444;
+	default:
+		break;
+	}
+
+	return 0;
+}
+
+static int tas2764_hwmon_read(struct device *dev,
+			      enum hwmon_sensor_types type,
+			      u32 attr, int channel, long *val)
+{
+	struct tas2764_priv *tas2764 = dev_get_drvdata(dev);
+	int ret;
+
+	switch (attr) {
+	case hwmon_temp_input:
+		ret = tas2764_read_die_temp(tas2764, val);
+		break;
+	default:
+		ret = -EOPNOTSUPP;
+		break;
+	}
+
+	return ret;
+}
+
+static const struct hwmon_channel_info *const tas2764_hwmon_info[] = {
+	HWMON_CHANNEL_INFO(temp, HWMON_T_INPUT),
+	NULL
+};
+
+static const struct hwmon_ops tas2764_hwmon_ops = {
+	.is_visible	= tas2764_hwmon_is_visible,
+	.read		= tas2764_hwmon_read,
+};
+
+static const struct hwmon_chip_info tas2764_hwmon_chip_info = {
+	.ops	= &tas2764_hwmon_ops,
+	.info	= tas2764_hwmon_info,
+};
+
 static int tas2764_codec_probe(struct snd_soc_component *component)
 {
 	struct tas2764_priv *tas2764 = snd_soc_component_get_drvdata(component);
@@ -825,6 +900,20 @@ static int tas2764_i2c_probe(struct i2c_client *client)
 		}
 	}
 
+	if (IS_REACHABLE(CONFIG_HWMON)) {
+		struct device *hwmon;
+
+		hwmon = devm_hwmon_device_register_with_info(&client->dev, "tas2764",
+							tas2764,
+							&tas2764_hwmon_chip_info,
+							NULL);
+		if (IS_ERR(hwmon)) {
+			return dev_err_probe(&client->dev, PTR_ERR(hwmon),
+					     "Failed to register temp sensor\n");
+		}
+	}
+
+
 	return devm_snd_soc_register_component(tas2764->dev,
 					       &soc_component_driver_tas2764,
 					       tas2764_dai_driver,

sound/soc/codecs/tas2764.h

@@ -117,6 +117,9 @@
 #define TAS2764_INT_LTCH3               TAS2764_REG(0x0, 0x50)
 #define TAS2764_INT_LTCH4               TAS2764_REG(0x0, 0x51)
 
+/* Readout Registers */
+#define TAS2764_TEMP                    TAS2764_REG(0x0, 0x56)
+
 /* Clock/IRQ Settings */
 #define TAS2764_INT_CLK_CFG             TAS2764_REG(0x0, 0x5c)
 #define TAS2764_INT_CLK_CFG_IRQZ_CLR    BIT(2)