ata_std_qc_defer not good enough for FIS-based switching ?

[Mark Lord <liml@rtr.ca>]

Tejun,

I've been trying to track down interrupt timeouts here with sata_mv,
and I think I've found the problem

With a Marvell 7042 chip and a port-multiplier, the driver selects
.qc_defer = ata_std_qc_defer, which is supposed to be correct for FIS-based switching.

But.. There is a mix of NCQ and non-NCQ drives plugged into that PM,
and ata_std_qc_defer() seems happy to mix things up by issuing NCQ commands
to some ports while simultaneously sending non-NCQ commands to other ports.

Needless to say, this confuses the heck out of the hardware,
which cannot tolerate non-NCQ commands in FIS-based switching mode,
or NCQ commands in non FIS-based switching mode.

Are there controllers which *can* handle such a mix (ahci, sil24 ?)

So it looks like a I need a .qc_defer() function which examines all links
from the common host port for activity, and then asks for command deferral
when the new command has a different protocol than those that are outstanding.

Weird that none of the other LLDs need this.  Or do they?

Cheers