link
spd_limit
Adjust SATA spd limit of link downward. Note that this function only adjusts the limit. The change must be applied using sata_set_spd.
If spd_limit is non-zero, the speed is limited to equal to or lower than spd_limit if such speed is supported. If spd_limit is slower than any supported speed, only the lowest supported speed is allowed.
0 on success, negative errno on failure
Jeff Garzik