If your a partner,  i think it is kept under EMC Service Partner Web.  Select the Software link and then "drive code" from the dropdown menu.
Hi, I am a working on a CX4-120 and need to upgrade disk firmware using USM. I have no access to the internet to download the firmware. I am a partner and cannot find the firmware on powerlink.  thanks Fred
Upgrade Disk firmware site is secure and no Internet access