If you upgrade your 840 firmware you will need to rebuild a custom
kernel with the proper ATA HORKAGE, as I do since the upgrade,
or you will need to use libata.force=noncq (which I discourage).
Don't know if and when the patch will be included in stock kernel,
but the latest (3.13.0-37-generic) still have this problem...
@Cyberbob, I'm in the same situation:
SSD 840 EVO and Linux Mint 17.1 Mate Edition...
If you upgrade your 840 firmware you will need to rebuild a custom
kernel with the proper ATA HORKAGE, as I do since the upgrade,
or you will need to use libata.force=noncq (which I discourage).
Don't know if and when the patch will be included in stock kernel,
but the latest (3.13.0-37-generic) still have this problem...
Hope for Mint 17.2 "Rafaela"...