rpmi: voltage: Clarify multi-linear format

Add explaination to multi-linear voltage format.

Signed-off-by: Joshua Yeong <[email protected]>

src/srvgrp-voltage.adoc

@@ -105,8 +105,16 @@ shows the structure of the simple-linear voltage format.
 |===
 
 ===== Multi-Linear Format
-Multiple linear ranges of voltage levels, each with its own step size. The
-following table shows the structure of the multi-linear voltage format.
+Multiple linear ranges of voltage levels, each with its own step size. This is
+useful for system with non-linear voltage or exponential voltage profiles for
+example [1000mV, 1250mV, 1500mV, 2000mV, 2500mV, 3000mV, 5000mV]. It will
+require 3 structures of multi-linear format to represent the voltage profile.
+
+        [1000000, 0, 2, 250000]
+        [1500000, 3, 5, 500000]
+        [3000000, 6, 7, 2000000]
+
+The following table shows the structure of the multi-linear voltage format.
 
 [cols="1,2,5" width=100%, align="center", options="header"]
 |===
@@ -120,11 +128,13 @@ following table shows the structure of the multi-linear voltage format.
 
 | 1
 | VOLTAGE_MIN_SEL
-| Lowest selector for range.
+| Lowest selector for range. This represent the base selector value
+corresponding to VOLTAGE_MIN.
 
 | 2
 | VOLTAGE_MAX_SEL
-| Highest selector for range.
+| Highest selector for range. This represent the maximum selector index with
+respect to VOTLAGE_MIN_SEL.
 
 | 3
 | STEP