jgarzik at pobox.com
Thu Aug 12 16:11:37 PDT 2004
* From the T10 Reflector (t10 at t10.org), posted by:
* Jeff Garzik <jgarzik at pobox.com>
Curtis Stevens wrote:
> My point is that the information is available to the bridge when the CDB is
> received. I do not think we want to get into specifying the intervening
> layers, there are many possible models. Software-wise, there is no
> difference between PIO multiple and PIO. In both cases the ATA host needs
> the DRQ block size. This will tell him how many blocks/interrupt to
In both my own software and in several vendor-written drivers, there
_is_ a difference in code paths between PIO and PIO-Mult. Just look at
the code that's out there.
> I also do not believe the transport can be separated from the CDB because
> this has the transfer length in addition to the direction. While I could
> place the protocol field in the CDB, there is no room for the length. The
> ATA host also needs this information to properly complete a PIO transfer.
> For DMA transfers, this information may also be necessary for buffer size
> allocation, although some implementations could do it without buffers.
Every ATA read/write command specifies transfer length and data
direction already. No need to store or derive that information elsewhere.
> The reason I included the goals is that, given the applications I stated,
> queuing is not required. I am a member of the drive product team and
> understand the limitations. However, support of queuing would require
> asynchronous status notification by the bridge to the application. I don't
> think we really need to go there at this time. If this pass-through becomes
> wildly successful and starts to be used in a performance environment, then
> we can upgrade it to provide more capability.
I would prefer that we get it right the first time ;-)
ATA passthru can and will be used to verify the correctness of the
underlying OS driver, bypassing all translation layers.
Lack of support for queueing, etc. prevents such verification.
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