diff --git a/core/java/android/os/ParcelFileDescriptor.java b/core/java/android/os/ParcelFileDescriptor.java
index 3212139b55b60..c091420a31d4e 100644
--- a/core/java/android/os/ParcelFileDescriptor.java
+++ b/core/java/android/os/ParcelFileDescriptor.java
@@ -547,7 +547,8 @@ public class ParcelFileDescriptor implements Parcelable, Closeable {
      * Converts a string representing a file mode, such as "rw", into a bitmask suitable for use
      * with {@link #open}.
      * <p>
-     * @param mode The string representation of the file mode.
+     * @param mode The string representation of the file mode. Can be "r", "w", "wt", "wa", "rw"
+     *             or "rwt".
      * @return A bitmask representing the given file mode.
      * @throws IllegalArgumentException if the given string does not match a known file mode.
      */
diff --git a/core/java/android/provider/DocumentsProvider.java b/core/java/android/provider/DocumentsProvider.java
index 2a83c4b6a6baa..3eef31ad56aa7 100644
--- a/core/java/android/provider/DocumentsProvider.java
+++ b/core/java/android/provider/DocumentsProvider.java
@@ -655,8 +655,12 @@ public abstract class DocumentsProvider extends ContentProvider {
      * <p>
      * Your provider should return a reliable {@link ParcelFileDescriptor} to
      * detect when the remote caller has finished reading or writing the
-     * document. You may return a pipe or socket pair if the mode is exclusively
-     * "r" or "w", but complex modes like "rw" imply a normal file on disk that
+     * document.
+     * <p>
+     * Mode "r" should always be supported. Provider should throw
+     * {@link UnsupportedOperationException} if the passing mode is not supported.
+     * You may return a pipe or socket pair if the mode is exclusively "r" or
+     * "w", but complex modes like "rw" imply a normal file on disk that
      * supports seeking.
      * <p>
      * If you block while downloading content, you should periodically check