Re: [PATCH v3 3/3] Add ata pass-through path for ZAC commands.

[Hannes Reinecke <hare@suse.de>]

On 06/10/2016 09:10 AM, Shaun Tancheff wrote:
> The current generation of HBA SAS adapters support connecting SATA
> drives and perform SCSI<->ATA translations in hardware.
> Unfortunately the ZBC commands are not being translate (yet).
> 
> Currently users of SAS controllers can only send ZAC commands via
> ata pass-through.
> 
> This method overloads the meaning of REQ_META to direct ZBC commands
> to construct ZAC equivalent ATA pass through commands.
> Note also that this approach expects the initiator to deal with the
> little endian result due to bypassing the normal translation layers.
> 
> Signed-off-by: Shaun Tancheff <shaun.tancheff@seagate.com>
> ---
> So this patch isn't the right way to work around hardware that is
> missing features (mixing ATA commands in SCSI interface code) it
> maybe useful for end users in the near term who have HBA SAS
> controllers that don't support ZBC <-> ZAC translations.
> 
And indeed, this patch isn't right.
It is just for a very specific SAS HBA (mpt2sas/mpt3sas).
Other SAS HBAs like isci and hisi_sas work just nicely here.
So a translation into a ATA_16 command is _wrong_.
If you need to do this you'll have to move it into the LLDD itself.
Or use blacklisting to invoke this behaviour.
But _not_ in the general code path.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
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