[PATCH v9 1/3] dt-bindings: thermal: imx: Document temperature offset property

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

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

Some boards need the reported temperature to reflect the SoC
package-surface temperature rather than the internal die temperature.

Document the optional fsl,temp-calibration-offset-millicelsius property,
a signed offset in millicelsius applied to the internally measured
temperature to make it better correspond to the package-surface
temperature. The offset is board-specific and is determined through
thermal characterization. When absent, the offset is zero.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Haoning CHENG <Haoning.CHENG@cn.bosch.com>
---
 .../devicetree/bindings/thermal/imx-thermal.yaml          | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/Documentation/devicetree/bindings/thermal/imx-thermal.yaml b/Documentation/devicetree/bindings/thermal/imx-thermal.yaml
index 949b154856c5..6c268d56291b 100644
--- a/Documentation/devicetree/bindings/thermal/imx-thermal.yaml
+++ b/Documentation/devicetree/bindings/thermal/imx-thermal.yaml
@@ -59,6 +59,20 @@ properties:
   clocks:
     maxItems: 1
 
+  fsl,temp-calibration-offset-millicelsius:
+    minimum: -20000
+    maximum: 20000
+    description:
+      A signed offset, in millicelsius, added to the calculated
+      sensor temperature to make the TEMPMON reading better correspond
+      to the SoC package-surface temperature observed during board-level
+      thermal characterization. This is not a sensor calibration offset;
+      it is a board-specific conversion offset derived from the
+      relationship between the internal sensor reading and the
+      package-surface temperature, which depends on the package, PCB
+      layout, cooling arrangement, and operating environment. The range
+      is limited to ±20 °C. When absent, no offset is applied.
+
   "#thermal-sensor-cells":
     const: 0
 
@@ -109,6 +123,7 @@ examples:
             nvmem-cells = <&tempmon_calib>, <&tempmon_temp_grade>;
             nvmem-cell-names = "calib", "temp_grade";
             clocks = <&clks IMX6SX_CLK_PLL3_USB_OTG>;
+            fsl,temp-calibration-offset-millicelsius = <(-6400)>;
             #thermal-sensor-cells = <0>;
         };
     };

-- 
2.43.0