hw.mfi.allow_cam_disk_passthrough missing?

[Zaphod Beeblebrox]

so... I see in my source (10.2-STABLE):

static int mfi_allow_disks = 0;
TUNABLE_INT("hw.mfi.allow_cam_disk_passthrough", &mfi_allow_disks);
SYSCTL_INT(_hw_mfi, OID_AUTO, allow_cam_disk_passthrough, CTLFLAG_RD,
    &mfi_allow_disks, 0, "event message locale");

... sysctl hw.mfi.allow_cam_disk_passthrough:

[1:6:306]root at virtual:~> sysctl hw.mfi.allow_cam_disk_passthrough
sysctl: unknown oid 'hw.mfi.allow_cam_disk_passthrough': No such file or
directory

even though this is a generic kernel that contains mfi and the card in
question probes up just fine.

What gives?