dt: thermal: tsens: Document the fallback DT property for v2 of TSENS IP

We want to create common code for v2 of the TSENS IP block that is used in
a large number of Qualcomm SoCs. "qcom,tsens-v2" should be able to handle
most of the common functionality start with a common get_temp() function.

It is also necessary to split out the memory regions for the TM and SROT
register banks because their offsets are not constant across SoC families.
Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Tested-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>

Documentation/devicetree/bindings/thermal/qcom-tsens.txt

 * QCOM SoC Temperature Sensor (TSENS)
 
 Required properties:
-- compatible :
- - "qcom,msm8916-tsens" : For 8916 Family of SoCs
- - "qcom,msm8974-tsens" : For 8974 Family of SoCs
- - "qcom,msm8996-tsens" : For 8996 Family of SoCs
+- compatible:
+  Must be one of the following:
+    - "qcom,msm8916-tsens" (MSM8916)
+    - "qcom,msm8974-tsens" (MSM8974)
+    - "qcom,msm8996-tsens" (MSM8996)
+    - "qcom,msm8998-tsens", "qcom,tsens-v2" (MSM8998)
+    - "qcom,sdm845-tsens", "qcom,tsens-v2" (SDM845)
+  The generic "qcom,tsens-v2" property must be used as a fallback for any SoC
+  with version 2 of the TSENS IP. MSM8996 is the only exception because the
+  generic property did not exist when support was added.
+
+- reg: Address range of the thermal registers.
+  New platforms containing v2.x.y of the TSENS IP must specify the SROT and TM
+  register spaces separately, with order being TM before SROT.
+  See Example 2, below.
 
-- reg: Address range of the thermal registers
 - #thermal-sensor-cells : Should be 1. See ./thermal.txt for a description.
 - #qcom,sensors: Number of sensors in tsens block
 - Refer to Documentation/devicetree/bindings/nvmem/nvmem.txt to know how to specify
 nvmem cells
 
-Example:
+Example 1 (legacy support before a fallback tsens-v2 property was introduced):
 tsens: thermal-sensor@900000 {
 		compatible = "qcom,msm8916-tsens";
 		reg = <0x4a8000 0x2000>;
@@ -20,3 +30,12 @@ tsens: thermal-sensor@900000 {
 		nvmem-cell-names = "caldata", "calsel";
 		#thermal-sensor-cells = <1>;
 	};
+
+Example 2 (for any platform containing v2 of the TSENS IP):
+tsens0: thermal-sensor@c263000 {
+		compatible = "qcom,sdm845-tsens", "qcom,tsens-v2";
+		reg = <0xc263000 0x1ff>, /* TM */
+			<0xc222000 0x1ff>; /* SROT */
+		#qcom,sensors = <13>;
+		#thermal-sensor-cells = <1>;
+	};