Date: Sun, 30 Mar 2008 21:29:06 +0900 (JST)
Message-Id: <20080330.212906.75185185.anemo@mba.ocn.ne.jp>
To: haavard.skinnemoen@atmel.com
Cc: david-b@pacbell.net, spi-devel-general@lists.sourceforge.net,
       linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
       marc.pignat@hevs.ch, nforrester@whoi.edu
Subject: Re: [PATCH] atmel_spi: support zero length transfer (resend)
From: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
In-Reply-To: <20080329175651.311b4f6d@hskinnemo-gx620.norway.atmel.com>
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	<20080329175651.311b4f6d@hskinnemo-gx620.norway.atmel.com>
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On Sat, 29 Mar 2008 17:56:51 +0100, Haavard Skinnemoen <haavard.skinnemoen@atmel.com> wrote:
> > Though some discussion about zero length transfer were raised by this
> > patch last time, I think there were no explicit objection to this
> > patch itself.
> 
> Well, the patch doesn't seem to do any harm, but I can't see much of a
> point to it either if zero-length transfers aren't going to be
> allowed...

Well, some wired device might want long delay before first CLK edge.
I think most device do not have such constraint, but ...

Anyway, SPI framework does not reject it.  So I think the controller
driver should accept it unless it is hard to support on that hardware.

> Also, if the length is zero, the driver will end up doing a memset with
> length zero at some point. Is that allowed?

I believe memset() with zero length should be allowed.  It seems
ambiguous that dma_sync_single_for_device() with zero length is legal
or not.  Actually, it seems OK on ARM and AVR32.

---
Atsushi Nemoto
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