dt-bindings: battery: Voltage drop properties

ROHM has developed a so called "zero-correction" -algorithm to improve
the fuel-gauging accuracy close to the point where battery is depleted.
This relies on battery specific "VDR" (voltage drop rate) tables, which
are measured from the battery, and which describe the voltage drop rate.
More thorough explanation about the "zero correction" and "VDR"
parameters is here:
https://lore.kernel.org/all/676253b9-ff69-7891-1f26-a8b5bb5a421b@fi.rohmeurope.com/

Document the VDR zero-correction specific battery properties used by the
BD71815, BD71828, BD72720 and some other ROHM chargers. (Note, charger
drivers aren't upstream yet).

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Link: https://patch.msgid.link/461f2840a03e0189ecd4f1a7c261014342ddee91.1765804226.git.mazziesaccount@gmail.com
Signed-off-by: Lee Jones <lee@kernel.org>

Author: M-Vaittinen

Documentation/devicetree/bindings/power/supply/battery.yaml

@@ -128,6 +128,21 @@ properties:
       - description: alert when battery temperature is lower than this value
       - description: alert when battery temperature is higher than this value
 
+  # The volt-drop* -properties describe voltage-drop for a battery, described
+  # as VDROP in:
+  # https://patentimages.storage.googleapis.com/6c/f5/17/c1d901c220f6a9/US20150032394A1.pdf
+  volt-drop-thresh-microvolt:
+    description: Threshold for starting the VDR correction
+    maximum: 48000000
+
+  volt-drop-soc-bp:
+    description: Table of capacity values matching the values in VDR tables.
+      The value should be given as basis points, 1/100 of a percent.
+
+  volt-drop-temperatures-millicelsius:
+    description: An array containing the temperature in milli celsius, for each
+      of the VDR lookup table.
+
 required:
   - compatible
 
@@ -146,6 +161,13 @@ patternProperties:
         - description: battery capacity percent
           maximum: 100
 
+  '^volt-drop-[0-9]-microvolt':
+    description: Table of the voltage drop rate (VDR) values. Each entry in the
+      table should match a capacity value in the volt-drop-soc table.
+      Furthermore, the values should be obtained for the temperature given in
+      volt-drop-temperatures-millicelsius table at index matching the
+      number in this table's name.
+
 additionalProperties: false
 
 examples: