On Mon, Jan 17, 2011 at 06:20:54PM +0100, Tejun Heo wrote:

On Mon, Jan 17, 2011 at 06:13:12PM +0100, Herbert Poetzl wrote:

quoted

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So perhaps it should be. If you look at the equivalent topology on
SAS, our expanders have a bsg device node precisely so that we can do
this.

I agree, the PMP should get a device or at least some kind of
interface to address them, especially as the SATA topology can
get quite complicated too, for example it seems that PMPs can
be daisy chained in an infinite sequence like this

       /      /      /
 --[PM]---[PM]---[PM]-- - -
       \      \      \

Oh, no, that's not allowed.  You can't address destinations that way.
PMP is primarily a switch, not a router.

hmm, haven't had the time to dig through the specs yet, but
at least addonics seems to disagree here:

http://www.addonics.com/products/host_controller/tutorial_pm.asp

but maybe that's just a marketing page with no relation
to reality ....

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Sure, as long as it speaks standard ses-2, there shouldn't be a
protocol problem. The main problem is recognition: ses has to bind
to an enclosure device. It can bind either to an explicit device
(about all the enclosures I've seen so far) where the ses device has
a separate address in the SCSI topology or an implicit device (where
another SCSI device indicates it has an enclosure port embedded in
it). As currently coded, our ses driver only does the former probably
the best way is to expose the ses device via libata and we'll simply
bind to it.

so AHCI em_messages use standard ses-2 or did I misinterpret
this (for me cryptical) information?

AFAIK, it just doesn't care.  It could be ses-2 or whatever else.  It
just transmits the binary blob it receives via sysfs and vice-versa.

the interesting part here is, that the AHCI host controller
my PMP is connected to recognizes the PMP perfectly fine
(i.e. more than one drive works just as expected), but doesn't
seem to allow for the em_message part (despite the fact that
the attached PMP seems to be SEMB/SEP capable) ...

maybe this is just a bug in the kernel code, maybe the AHCI
implementation doesn't allow a PMP to receive enclosure
management messages at all ...

best,
Herbert

Thanks.

-- 
tejun