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

[Jeff Garzik <jeff@garzik.org>]

Brian King wrote:
> 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.

I'm generally happy with this, though I am curious what Tejun thinks as 
well.

Once everybody is happy, I think we should collect libata ACKs and then 
push this via the SCSI maintainership route.  That would libsas work in 
parallel, with perhaps in situ tweaks and fixes as the implementation is 
fleshed out.

	Jeff