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

Open Source and information security mailing list archives

Date:	Fri, 14 Sep 2012 08:57:59 +0530
From:	Vinod Koul <vkoul@...radead.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	vinod.koul@...el.com, Lars-Peter Clausen <lars@...afoo.de>,
	alsa-devel@...a-project.org,
	Janusz Krzysztofik <jkrzyszt@....icnet.pl>,
	Tony Lindgren <tony@...mide.com>,
	Ricardo Neri <ricardo.neri@...com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	linux-kernel@...r.kernel.org,
	Peter Ujfalusi <peter.ujfalusi@...com>,
	linux-arm-kernel@...ts.infradead.org, Dan Williams <djbw@...com>,
	linux-omap@...r.kernel.org, Liam Girdwood <lrg@...com>,
	Jarkko Nikula <jarkko.nikula@...mer.com>
Subject: Re: [PATCH v2 03/15] dmaengine: Add no_wakeup parameter to
 dmaengine_prep_dma_cyclic()

On Thu, 2012-09-13 at 16:38 +0100, Russell King - ARM Linux wrote:
> On Thu, Sep 13, 2012 at 05:27:09PM +0200, Lars-Peter Clausen wrote:
> > Hm... Do you think it would work as well if we implement this by setting the
> > callback for the descriptor to NULL? If the callback is NULL there is
> > nothing to at the end of a transfer/period and the dma engine driver may
> > choose to disable interrupts. This would also benefit non cyclic transfers
> > where the callback is NULL and we do not need add the new parameter to
> > dmaengine_prep_dma_cyclic.
> 
> Actually, there's a way to do that already.  DMA_PREP_INTERRUPT.
> Unfortunately, most DMA engine slave API users don't set it when they
> setup their transfer:
> 
>  * @DMA_PREP_INTERRUPT - trigger an interrupt (callback) upon completion of
>  *  this transaction
Looks like I have repeated the correct action!
> 
> if we fixed that, then we could use the lack of it to avoid the interrupt.
> 
> However, cyclic transfers don't have the flags parameter used to pass this
> bit.  Yet another bit of yucky inconsistent design in DMA engine land...
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel


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