Re: REQ_PM vs REQ_TYPE_PM_RESUME

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On 1/9/2014 1:29 PM, Douglas Gilbert wrote:
> When REQUEST SENSE had its original semantics, TEST UNIT READY was
> the only game in town for monitoring power management. From my
> reading of spc4r36n.pdf section  5.1.2 "Important commands for all
> SCSI device servers" TEST UNIT READY should be called before
> REQUEST SENSE during device initialization (including resume). If
> the responses to TEST UNIT READY and REQUEST SENSE contradict then
> the former is correct.

I don't see language there remotely like that.  How did you arrive at
this conclusion?

> There are SCSI devices out caught in that transition. For example
> with sg_format I monitor progress with either TEST UNIT READY or
> REQUEST SENSE, defaulting to the former. [Progress indication is
> another new role for REQUEST SENSE.]
> 
> Note that the billion or so USB keys out there that say that they
> comply with SCSI-2 should respond to a REQUEST SENSE with its
> original semantics.

Then they will return 0/0/0, so we will assume they are up and
running, which is correct.  SPC-2 is coming up on 13 years old and
listed this usage for REQUEST SENSE.  Are there any actual disk drives
out there ( and still in use ) that return 0/0/0 when in the stopped
state?  I can't imagine there would be.

> The ATA REQUEST SENSE DATA EXT command refers to the SPC-4 
> "standard" (not yet it ain't) which is naturally the new SCSI
> semantics of REQUEST SENSE. I believe the ATA REQUEST SENSE DATA
> EXT command is a relatively new ATA command so it does not carry
> the historical baggage of its SCSI counterpart.

It is also only for ATAPI devices.


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