[PATCH v9 3/3] thermal/drivers/imx: Add temperature offset support

[Haoning CHENG via B4 Relay <devnull+Haoning.CHENG.cn.bosch.com@kernel.org>]

From: Haoning CHENG <Haoning.CHENG@cn.bosch.com>

Some boards need a small per-design offset to make the TEMPMON reading
better correspond to the SoC package-surface temperature. This is not a
sensor calibration that improves the die temperature accuracy; it is a
board-specific conversion from the internal sensor reading to a
package-surface temperature estimate required by certain applications.

Read the optional fsl,temp-calibration-offset-millicelsius property from
DT and apply it uniformly to the i.MX6/6SX/7D formulas.

The offset is applied symmetrically at two points to keep the trip point
semantics consistent:

1. In imx_set_alarm_temp() and imx_set_panic_temp(): the temperature
   threshold is *subtracted* by the offset before being converted to a
   hardware register value. This shifts the hardware IRQ trigger to the
   die temperature that corresponds to the intended package-surface
   threshold.

2. In imx_get_temp(): after computing the die temperature from the
   hardware register, the offset is *added* to produce a value that
   better correlates with the package-surface temperature. The thermal
   framework always sees this package-surface estimate.

For example, if DT sets offset = +3000 m°C and the passive trip is 95°C:

  imx_set_alarm_temp(95000):
    alarm_temp = 95000 - 3000 = 92000
    → hardware register programmed for 92°C die temperature

  Hardware IRQ fires at 92°C die temperature

  imx_get_temp():
    reads hardware, computes 92°C die temperature
    *temp = 92000 + 3000 = 95000
    → thermal framework sees 95°C → correct trip

When the property is not present, the offset defaults to 0, preserving
the current behavior.

Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Haoning Cheng <Haoning.CHENG@cn.bosch.com>
---
 drivers/thermal/imx_thermal.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/drivers/thermal/imx_thermal.c b/drivers/thermal/imx_thermal.c
index 7f7d1116b9d6..d471acc16bce 100644
--- a/drivers/thermal/imx_thermal.c
+++ b/drivers/thermal/imx_thermal.c
@@ -85,6 +85,10 @@ enum imx_thermal_trip {
 #define TEMPMON_IMX6SX			2
 #define TEMPMON_IMX7D			3
 
+/* Calibration offset limits (±20 °C in millicelsius) */
+#define IMX_TEMP_CALIB_OFFSET_MIN	(-20000)
+#define IMX_TEMP_CALIB_OFFSET_MAX	20000
+
 struct thermal_soc_data {
 	u32 version;
 
@@ -207,6 +211,7 @@ struct imx_thermal_data {
 	struct regmap *tempmon;
 	u32 c1, c2; /* See formula in imx_init_calib() */
 	int temp_max;
+	s32 calibration_offset;
 	int alarm_temp;
 	int last_temp;
 	bool irq_enabled;
@@ -223,6 +228,7 @@ static void imx_set_panic_temp(struct imx_thermal_data *data,
 	struct regmap *map = data->tempmon;
 	int critical_value;
 
+	panic_temp -= data->calibration_offset;
 	critical_value = (data->c2 - panic_temp) / data->c1;
 
 	regmap_write(map, soc_data->panic_alarm_ctrl + REG_CLR,
@@ -239,6 +245,7 @@ static void imx_set_alarm_temp(struct imx_thermal_data *data,
 	int alarm_value;
 
 	data->alarm_temp = alarm_temp;
+	alarm_temp -= data->calibration_offset;
 
 	if (data->socdata->version == TEMPMON_IMX7D) {
 		if (alarm_temp >= 0)
@@ -283,6 +290,7 @@ static int imx_get_temp(struct thermal_zone_device *tz, int *temp)
 		*temp = (n_meas - data->c1 + 25) * 1000;
 	else
 		*temp = data->c2 - n_meas * data->c1;
+	*temp += data->calibration_offset;
 
 	/* Update alarm value to next higher trip point for TEMPMON_IMX6Q */
 	if (data->socdata->version == TEMPMON_IMX6Q) {
@@ -635,6 +643,25 @@ static int imx_thermal_probe(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, data);
 
+	if (of_property_present(dev->of_node,
+				"fsl,temp-calibration-offset-millicelsius")) {
+		ret = of_property_read_s32(dev->of_node,
+					   "fsl,temp-calibration-offset-millicelsius",
+					   &data->calibration_offset);
+		if (ret)
+			return dev_err_probe(dev, ret,
+					     "failed to read calibration offset\n");
+
+		if (data->calibration_offset < IMX_TEMP_CALIB_OFFSET_MIN ||
+		    data->calibration_offset > IMX_TEMP_CALIB_OFFSET_MAX)
+			return dev_err_probe(dev, -EINVAL,
+					     "calibration offset %d millicelsius out of range\n",
+					     data->calibration_offset);
+
+		dev_dbg(dev, "calibration offset: %d millicelsius\n",
+			data->calibration_offset);
+	}
+
 	if (of_property_present(dev->of_node, "nvmem-cells")) {
 		ret = imx_init_from_nvmem_cells(pdev);
 		if (ret)

-- 
2.43.0