From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH] megaraid_sas: Enable shared tag map
Date: Thu, 2 Oct 2014 02:19:16 -0700
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To: Hannes Reinecke <hare@suse.de>
Cc: Christoph Hellwig <hch@infradead.org>, Webb Scales <webbnh@hp.com>, James Bottomley <jbottomley@parallels.com>, linux-scsi@vger.kernel.org

On Thu, Oct 02, 2014 at 08:51:20AM +0200, Hannes Reinecke wrote:
> 
> I'm afraid it's not _that_ easy.
> SCSI-II tagged queueing has some specific tag values:
> 
> #define SIMPLE_QUEUE_TAG    0x20
> #define HEAD_OF_QUEUE_TAG   0x21
> #define ORDERED_QUEUE_TAG   0x22

These are not tag values.  These are message codes set in the first byte
of the Queue tag message, the second byte is the actual tag.

> The recommendation here is to use 'scmd->request->tag' whenever
> you want to get to the tag number, and 'scmd->tag' if you have to
> play around with SCSI-II TCQ.
> But if not I would strongly advise to leave 'scmd->tag' alone.

Or kill off scmd->tag..  Let's see how feasible that is.