Re: [PATCH 9/13] mpt2sas: T10 DIF Support - EEDP

["Martin K. Petersen" <martin.petersen@oracle.com>]

>>>>> "Eric" == Moore, Eric <Eric.Moore@lsi.com> writes:

Eric,

Eric> The SAS controller firmware checks the tags, not device driver.
Eric> What this code is doing is setting flags in the SCSI_IO Request
Eric> message that is being sent to controller firmware.

Yeah, I figured that much.  I guess it makes sense when you treat the
app tag as being constant (modulo the mask) for one request.


Eric> Obviously the only errors the current implementation will only be
Eric> flaged on READs.

Eric> My line of thinking was I write the code so it won't need to be
Eric> rewrote later when DIX support is added for SAS3.0.

Ok, that's fine then.


Eric> Yes, I was told by the LSI software test lab, they saw drives
Eric> returning check condition with these ref tag errors.  I wasn't
Eric> able to repro that.  What I saw were the IOCSTATUS errors, which
Eric> is what the code handles in _scsih_eedp_error_handling().  Either
Eric> way, both cases are covered right?

Yeah.  With READ the difference is mostly academic.


>> If I understand correctly, your firmware only deals with the Type 2
>> usage model of the application tag.  And Type 1 + 2 usage of the
>> reference tag.

Eric> Our controller firmware support all three types of protection..

So you can actually set the application tag (and reference tag) on a
per-sector basis for Type 1 and 3 provided the OS sends down 520-byte
sectors?


>> + scsi_host_set_guard(shost, SHOST_DIX_GUARD_CRC);
>> 
>> Technically speaking that is only required for DIX exchange.  But
>> setting it doesn't hurt.

Eric> I wasn't sure whether it needed to be set.  Our controller
Eric> generates the CRC. I'm not sure whether firmware or hardware
Eric> implementation.

Given that it sounds like your next chip rev. will use the same driver
it should be ok to leave it in place.

-- 
Martin K. Petersen	Oracle Linux Engineering