More descriptions on SubscriptionController#setPreferredData

Bug: 115550764
Test: build
Change-Id: I25c3f89a3c3f8e8e6475221885d995bcb5684da4

1 files changed, 6 insertions, 1 deletions

diff --git a/telephony/java/android/telephony/SubscriptionManager.java b/telephony/java/android/telephony/SubscriptionManager.java
index b01d41948c3b..d4da58974c90 100644
--- a/telephony/java/android/telephony/SubscriptionManager.java
+++ b/telephony/java/android/telephony/SubscriptionManager.java
@@ -2117,7 +2117,12 @@ public class SubscriptionManager {
 
     /**
      * Set preferred default data.
-     * Set on which slot default data will be on.
+     * Set on which slot most cellular data will be on.
+     * It's also usually what we set up internet connection on.
+     *
+     * PreferredData overwrites user setting of default data subscription. And it's used
+     * by ANAS or carrier apps to switch primary and CBRS subscription dynamically in multi-SIM
+     * devices.
      *
      * @param slotId which slot is preferred to for cellular data.
      * @hide