Buffalo WHR-AMG54

Overview
On wifi.com.cn (internal images)
 * "WHR4-AG54A REV: XC" and a date code of 0542 is silkscreened on the board.
 * The format would seem to indicate CyberTAN manuf

On the OpenWrt forums

Per the DD-WRT Supported Devices table, you can use the WHR-HP-G54 firmware.