[RFC 0/3] [SCSI/libata] libata EH conversion for ipr SAS

[Brian King <brking@linux.vnet.ibm.com>]

The following three patches convert ipr to use the new libata EH APIs.
In the process of doing this, I first looked into implementing this
in a similar manner to how libata SAS is done today, which is hooking
into target_alloc/target_destroy to allocate/delete sata ports. While
I was able to get this working after writing my own eh_strategy_handler,
I was doubtful this was the best long term solution. One problem with this
implementation I didn't solve was the fact that libata now invokes EH
for each and every error received. For some devices, such as optical
devices, each not ready response received during a media reload would
result in all the attached SAS devices getting quiesced as well.

My second approach is the attached patch set. In this series I have
created a new libata API which can be used by SAS LLDDs. It introduces
an ata_sas_rphy device object which is created/destroyed by the following API:

ata_sas_rphy_alloc
ata_sas_rphy_add
ata_sas_rphy_delete

When using this API in ipr, I made ipr's scsi_host the parent device of the
SATA rphy. The SATA rphy is then the parent of the allocated scsi_hosts. This
means that each SATA rphy in the SAS topology will have its own scsi_host, making
SAS *much* more like all the SATA LLDDs in how it uses libata.

The only issue I ran into with this implementation is that since each SATA
port has its own scsi_host, the adapter cannot rely on scsi core to manage
any LLDD or adapter imposed queue depth. To solve this I added some code to
ipr. Longer term, block layer queue groups might be another way to do this.

I'm still polishing this up, but it is up and running and seems to work with
what testing I've done so far.

-Brian

-- 
Brian King
Linux on Power Virtualization
IBM Linux Technology Center