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   @@ -4289,26 +4294,16 @@ void ata_scsi_scan_host(struct ata_port
*ap, int sync)
    repeat:

I've been trying to follow this thread, below, but got a bit lost ....

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       ata_for_each_link(link, ap, EDGE) {
           ata_for_each_dev(dev, link, ENABLED) {
-            struct scsi_device *sdev;
+            struct Scsi_Host *shost = ap->scsi_host;
               int channel = 0, id = 0;
   -            if (dev->sdev)
-                continue;
-
               if (ata_is_host_link(link))
                   id = dev->devno;
               else
                   channel = link->pmp;
   -            sdev = __scsi_add_device(ap->scsi_host, channel, 
id, 0,
-                         NULL);
-            if (!IS_ERR(sdev)) {
-                dev->sdev = sdev;
-                ata_scsi_assign_ofnode(dev, ap);

Is there something equivalent to what this function does inside
scsi_scan_target() ? I had a quick look but did not see anything...

So are we discussing below whether we can have fixed channel, id, lun 
per ATA sdev per shost? If so, I don't think it would work as libsas 
uses dynamic target ids per host.

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Typically, the SCSI layer has two ways of scanning.
One it the old-style serial scanning (originating in the old SCSI
parallel model):
The scanning code will blindly scan _all_ devices up to max_luns, and
attach every device for which the scanning code returns 'OK'.
The other one is to issue REPORT_LUNS and scan all LUNs returned there.

Mapped to libata we would need to figure out a stable SCSI enumeration,
given that we have PMP and slave devices to content with.
To my knowledge we have ATA ports, each can have either a 'master' and
'slave' device, _or_ it be a PMP port when it can support up to 16
devices, right?

yes

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Point being, master/slave and PMP are exclusive, right?

Never heard of pmp with ide cable :)

See?

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So we can make the master as LUN 0, and the slave as LUN 1.

Yes, but isn't that a little wrong ? That would assume that the ata port
is the device and the ata devices the luns of that device. But beside
the "link busy" stuff that needs to be dealt with, master and slave are
independent devices, unlike LUNs. No ?
Well; technically, yes.

But we already enumerate the ata ports (which is typically done by the 
hardware/PCI layer etc), and if we were try to model slave devices as 
independent ports we would either have to insert a numbering (awkward) 
or add a number at the en (even more awkward).

And the one key takeaway from the 'multiple actuators' discussion is 
that LUNs _are_ independent (cf all the hoops they had to jump through 
to define a command spanning several LUNs ...)(which, incidentally, we 
could leverage here, too ...), and the target port really only serves as 
an enumeration thingie to address the LUNs.

So we _could_ map the master device on LUN 0 and the slave device on LUN 
1 with no loss of functionality, _but_ enable a consistent SCSI enumeration

Thanks,
John