linux-kernel - Re: [PATCH 9/9] tcm_qla2xxx: Add special case for COMPARE_AND_WRITE data

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Message-ID: <20130821160450.GA30848@infradead.org>
Date:	Wed, 21 Aug 2013 09:04:50 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Cc:	Christoph Hellwig <hch@...radead.org>,
	"Nicholas A. Bellinger" <nab@...erainc.com>,
	target-devel <target-devel@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	Christoph Hellwig <hch@....de>, Hannes Reinecke <hare@...e.de>,
	Martin Petersen <martin.petersen@...cle.com>,
	Chris Mason <chris.mason@...ionio.com>,
	James Bottomley <JBottomley@...allels.com>,
	Giridhar Malavali <giridhar.malavali@...gic.com>,
	Chad Dupuis <chad.dupuis@...gic.com>
Subject: Re: [PATCH 9/9] tcm_qla2xxx: Add special case for COMPARE_AND_WRITE
 data_direction

On Wed, Aug 21, 2013 at 12:31:07AM -0700, Nicholas A. Bellinger wrote:
> Is it really worth having two se_cmd_flags for COMPARE_AND_WRITE..?

Not leaking the abstraction into the driver is always worth the effort.

But looking at the other patches I haven't reviewed yet I think the
issue is more severe anyway, see my next reply.

> > Also it might make sense to lift this helper to get a dma direction from
> > a command into common code.
> > 
> 
> Mmm, perhaps.  I don't recall of the top of my head why tcm_qla2xxx
> actually needed to reverse it's dma direction (I'm sure that Roland
> knows, CC'ed), but IIRC it was a tcm_qla2xxx specific thing..?

It's the same issue for any hardware driver that directly maps a
se_cmd - the direction the target expects is reversed to what the
driver expects, in addition any BIDI or other special meanings will
need handling.

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