Re: [RFC/PATCH] Deferred disk spinup during system resume

[Jeff Garzik <jgarzik@pobox.com>]

On 01/13/2011 10:37 AM, Tejun Heo wrote:
> Hey, Jeff.
>
> On Wed, Jan 12, 2011 at 01:35:07PM -0500, Jeff Garzik wrote:
>> The previous patch breaks READ VERIFY translation for all cases
>> -except- this one.
>
> Ooh, right; then, can we just fix that?
>
>> The bottom line is that this patch simply wants to trigger an ATA
>> command, and return immediately, discarding the command results.
>> I'm not even sure a "run this command in background, and discard
>> results" facility requires the EH.
>
> It doens't necessarily require EH but the dependency is rather
> delicate because we still ride on SCSI EH.  For example, we don't have
> any provision for running qc's without the associated scmd.  If the
> command fails, libata EH rides on SCSI EH and the interaction relies
> on the association between qc's and scmd's.  We may be able to add
> privison for this case but we already have working mechanism in EH for
> internal commands so it's just easiser that way.

In this case we -do- have an associated scmd, otherwise he would not be 
able to trigger the READ VERIFY translation code.

So it seems a question of (a) who generates READ VERIFY, and (b) can we 
have them issue the command without waiting for the results?

Which is something I would have thought SG_IO/bsg already provided...

It remains unclear to me why EH must be updated, simply to execute a 
non-data ATA command without waiting.

	Jeff