After upgrading my MBP to OSX Yosemite and enabling TRIM, the computer cannot boot into the system after restart. It stuck with a no-entry sign.
You can solve this issue by following instructions from http://www.cindori.org/trim-in-os-x-yosemite/
Boot your Mac in Recovery Mode by holding Cmd-R during boot
Open the Terminal from the menu bar
Run these commands, replacing YourDisk with the name of your Mac disk
rm -rf /Volumes/YourDisk/System/Library/Extensions/IOAHCIFamily.kext
cp -r /System/Library/Extensions/IOAHCIFamily.kext /Volumes/YourDisk/System/Library/Extensions/IOAHCIFamily.kext
kextcache -u /Volumes/YourDisk
For me, I have to first use the disk utility to unlock my SSD first since I have Filevault enabled, otherwise the first command above will complain about “readonly” files.
Since TRIM is very helpful for SSDs, it’s encouraged to have it enabled for better performance. You can use Trim Enabler v3.2.5 and above without issues. But note that it disables kext signing on your mac, “it still leaves you with the same amount of security as in OS X Mavericks, where the kext signing requirement didn’t exist”. (http://www.cindori.org/update-on-trim-in-yosemite/)