Hello, Robert. Robert Hancock wrote: [--snip--]
On the NCQ side, I think it's pretty safe to assume that all controllers will handle it. Obviously I've verified it with sata_nv (at least that it doesn't blow up obviously), and the other two NCQ drivers we have, ahci and sata_sil24 just feed raw FIS data into the controller so there should be no issue with not supporting it.
FWIW, ICH6/7/8 ahci's clear PMP field when transmitting FIS. The reason why I'm hesitant is because there is no way to tell whether the FUA bit got honored or ignored. With extra opcode, it's okay because barrier explicitly fails but if NCQ FUA is not supported, it will succeed silently as normal write. Everything will be okay generally but the barrier is done incorrectly and on a really bad day it will lead to journal corruption.
So, actually, I was thinking about *always* using the non-NCQ FUA opcode. As currently implemented, FUA request is always issued by itself, so NCQ doesn't make any difference there. So, I think it would be better to turn on FUA on driver-by-driver basis whether the controller supports NCQ or not.
Well, I might be being too paranoid but silent FUA failure would be really hard to diagnose if that ever happens (and I'm fairly certain that it will on some firmwares).
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