U2415, apple DaisyChain sleep/wakeup issue

Hi,

In December 2014 I've purchased my Dell U2415. With my Macbook Pro 15 2011 sometimes my monitor doesn't wake up from sleep. With my Macbook Pro 15 2015 instead, If I activate DP 1.2, OSX Yosemite doesn't recognize my monitor. Using Windows I had no problem. My monitor is a REV 00. Is there any firmware update? How can I solve my problem?