Re: [PATCH] SATA NCQ support

[Jens Axboe <axboe@suse.de>]

On Fri, May 27 2005, Jeff Garzik wrote:
> Jens Axboe wrote:
> >That is the typical case, ata_qc_new() succeeds but we cannot issue the
> >command yet. So where do you want this logic placed? You cannot drop the
> >host_lock in-between, as that could potentially change the situation.
> 
> ata_scsi_translate() in libata-scsi.c, in between the call to 
> ata_scsi_qc_new() and ata_qc_issue().
> 
> something like:
> 
> 	if (ata_scsi_qc_new() fails ||
> 	    (depth > 0 && ata_check_non_ncq_cmd()))
> 		complete SCSI command with 'queue full'

That is an improvement for SCSI originated commands, I can drop
ATA_QCFLAG_DEFER then. Will make that change. But what about
ata_qc_issue() from other places? That is the ugly code, which will hit
the waiting currently.

> NOTE!
> 
> I just noticed a bug -- When ata_scsi_qc_new() fails, the code should 
> complete the command with queue-full, but does not.
> 
>         qc = ata_scsi_qc_new(ap, dev, cmd, done);
>         if (!qc)
>                 return;

Indeed, looks like an old bug.

-- 
Jens Axboe