linux-kernel - Re: Dmaengine query

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Date:	Wed, 14 Apr 2010 17:30:39 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	rd bairva <rbairva@...il.com>
Cc:	linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-kernel@...r.kernel.org
Subject: Re: Dmaengine query

On Tue, Apr 13, 2010 at 11:26 PM, rd bairva <rbairva@...il.com> wrote:
> Hi Dan,
>
>        I am currently writing dmaengine compatible DMA driver for our ARM
> based architecture, But I am facing some performance issues doing
> that.
>
> 1. dmaengine says callback should run in tasklet, and next transfer
> cannot be scheduled from the callback.
>
> Due to these restrictions I am getting some performance issue while
> playing sound in our architecture.
>
>
> Can callback call in DMA driver be placed out of spin_lock to submit
> new operations from callback? (only in asynchronous case)
>
> is this Ok? please comment.

Other dma driver authors are dropping the lock across the call to the
callback in the mem-to-io case.  The compliance points in the
documentation are primarily targeted at the expectations of the
async_tx api.  In the mem-to-io (slave dma) model you are not using
the async_tx api.

--
Dan
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