linux-kernel - Re: [PATCH v2 03/15] dmaengine: Add no_wakeup parameter to dmaengine_prep_dma

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Date:	Fri, 14 Sep 2012 12:28:28 +0300
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Vinod Koul <vinod.koul@...ux.intel.com>
CC:	Lars-Peter Clausen <lars@...afoo.de>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...com>, Tony Lindgren <tony@...mide.com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Dan Williams <djbw@...com>,
	Jarkko Nikula <jarkko.nikula@...mer.com>,
	alsa-devel@...a-project.org, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Janusz Krzysztofik <jkrzyszt@....icnet.pl>,
	Ricardo Neri <ricardo.neri@...com>
Subject: Re: [PATCH v2 03/15] dmaengine: Add no_wakeup parameter to dmaengine_prep_dma_cyclic()

Hi,

On 09/14/2012 11:50 AM, Vinod Koul wrote:
>> Well, the idea was that the driver would disable interrupts if there is no
>> callback to call, since there would be nothing to do in the interrupt
>> handler anyway. But I guess the flags approach should work fine as well.
> Yes we _could_ do that, but this relies on dmaengine driver to have this
> implicit understanding. Anyone using dmaengine library in ASoC may or
> may not be aware of this, so i would consider it hackish.
> 
> Using this flag explicitly makes everyone aware what the intended
> behaviour is.

I'm not sure about which flags should ASoC set for the two case we are going
to have. I think it should be something like this:

unsigned long flags = DMA_CTRL_ACK;

if (!substream->runtime->no_period_wakeup)
	flags |= DMA_PREP_INTERRUPT;

I'm not 100% sure of the role of DMA_CTRL_ACK in this case. Or should we only
handle the DMA_PREP_INTERRUPT flag, like this:

unsigned long flags = 0;

if (!substream->runtime->no_period_wakeup)
	flags |= DMA_PREP_INTERRUPT;


What do you think?

-- 
Péter
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