linux-kernel - Re: [PATCH 2/2] DMAENGINE: generic channel status

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Message-ID: <Pine.LNX.4.64.1003252334190.4413@axis700.grange>
Date:	Thu, 25 Mar 2010 23:37:14 +0100 (CET)
From:	Guennadi Liakhovetski <g.liakhovetski@....de>
To:	Dan Williams <dan.j.williams@...el.com>
cc:	Linus Walleij <linus.walleij@...ricsson.com>,
	linux-kernel@...r.kernel.org,
	Maciej Sosnowski <maciej.sosnowski@...el.com>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Pavel Machek <pavel@....cz>, Li Yang <leoli@...escale.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Haavard Skinnemoen <haavard.skinnemoen@...el.com>,
	Magnus Damm <damm@...nsource.se>,
	Liam Girdwood <lrg@...mlogic.co.uk>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Joe Perches <joe@...ches.com>,
	Roland Dreier <rdreier@...co.com>
Subject: Re: [PATCH 2/2] DMAENGINE: generic channel status

On Thu, 25 Mar 2010, Dan Williams wrote:

> On Thu, Mar 25, 2010 at 1:58 PM, Guennadi Liakhovetski
> <g.liakhovetski@....de> wrote:
> > On Thu, 25 Mar 2010, Linus Walleij wrote:
> >
> >> Convert the device_is_tx_complete() operation on the
> >> DMA engine to a generic device_tx_status()operation which
> >> can return three states, DMA_TX_RUNNING, DMA_TX_COMPLETE,
> >> DMA_TX_PAUSED.
> >>
> [..]
> > General: you converted all drivers to the new .device_tx_status() API, but
> > since they don't implement "residue," you left it uninitialised
> > everywhere. Wouldn't it be better to set it to 0 or total length,
> > depending on the complete / not complete status?
> 
> Agree that it should not be uninitialized.  At the same time I do not
> want to require drivers that don't need it to go through the hassle of
> looking up a byte count, so perhaps all but the drivers that want this
> support can return a 'max byte count'??

Why not assign one of the two - 0 if the transfer is complete (DMA_SUCCESS 
status returned) or whatever max count otherwise? Except I do think this 
might confuse some users - seeing a residue larger than the total transfer 
length...

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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