Stefan Smietanowski wrote:
Which is understandable considering AHCI doesn't construct FISes itself.
I don't think PM requires more hardware support than being capable for
setting PMP in the FISes, which AHCI certainly can (standing down on
collision for SDB notify aside). I can give it a shot but it clearly
violates the spec, and even if it works, we would need to print big fat
warning message while attaching PM.
Are you saying that the next big thing since sliced bread (AHCI) that's
supposed to unite the world and make everybody sing Kumbayah doesn't
support port multipliers (according to the spec) ?
Or am I totally misreading this.
Heh heh.
I love AHCI too, but as far as PMS is concerned, AHCI is not saving any
world. There's a bit called SPM (supports Port Multiplier) in the
capability register. If the bit is set, AHCI support PM by
command-based switching, which ummm... sucks - only one device can have
active commands at any given time. AHCI v1.1 (the current spec) lists
FIS-based switching PMS as 'to be specified in a future AHCI specification'.
To make matters worse, not many AHCI controllers seem to have that bit
set. My ICH7R (P5LD2) doesn't and I would be surprised if any of
ICH6R/M and ICH7M have that bit set. Zhao reported that ESB2 (server
chipset w/ 6 SATA ports) have that bit set, so there are some
controllers supporting PM out there.
However, cmd-switching PMS doesn't require much support from HBA, and I
don't see why my ICH7R cannot do PMS. I'm currently giving it a try now.
So, ATM, if you want PMS, sil3124/3132 series is the best choice.
--
tejun
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