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

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Message-ID: <e9c3a7c21003251705o63687fa5vfbe77ebeda8c0440@mail.gmail.com>
Date:	Thu, 25 Mar 2010 17:05:20 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
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, Mar 25, 2010 at 3:37 PM, Guennadi Liakhovetski
<g.liakhovetski@....de> wrote:
> 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...
>

0 if complete makes sense and then the actual residue or all 0xf's to
indicate "I don't support inflight residue reporting".

--
Dan
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