MySQL SP parameter for IN clause

Recently, I came across a question on stackoverflow.com where the poster indicated that he was not able to use the parameter string as part of stored procedure IN clause to get the right results and the result set always returned one row only.

Test table used for procedure:

CREATE TABLE cities (
  id int(10) unsigned NOT NULL auto_increment,
  name varchar(100) NOT NULL,
  PRIMARY KEY  (`id`)
);
insert into cities (name) values 
 ('London'), ('Manchester'), ('Bristol'), 
 ('Birmingham'), ('Brighton');

Original stored procedure:

DROP PROCEDURE IF EXISTS `cities_select_by_ids` $$
CREATE PROCEDURE `cities_select_by_ids`(
    in _cityIds varchar(1000)
)
BEGIN
SET  @cityIds = _cityIds;

PREPARE stmt FROM '
    select
      id,
      name
    from cities
    where id in (?);
';

EXECUTE stmt USING @cityIds;
DEALLOCATE PREPARE stmt;

END $$
DELIMITER ;

call cities_select_by_ids_prepare('1, 2, 3');
#-- Only 1 city name returned (London).

One work around would be to split the string into individual elements and run the select as below.

DROP PROCEDURE IF EXISTS `cities_select_by_ids_2` ;
CREATE PROCEDURE `cities_select_by_ids_2`(
    in cityIDs varchar(1000)
)
BEGIN

#- ix - index into the list of city IDs
#- cid - city ID
SET @ix := 1;
SET @cid := substring_index(cityIDs, ',', @ix);

LOOP_1: 
WHILE (@cid is not null) DO
    SELECT id,  name 
    FROM cities
        WHERE id in (@cid) ;
  
     #-- substring_index returns complete cityIDs string when index is > number of elements
     IF (length(substring_index(cityIDs, ',', @ix)) >= length(cityIDs)) THEN
          LEAVE LOOP_1;
     END IF;
     
     SET @ix := @ix + 1;
     SET @cid = substring_index(substring_index(cityIDs, ',', @ix), ',', -1);

END WHILE;
END 

#----
call cities_select_by_ids_2('1, 2, 3');