linux-kernel - Re: [PATCH v2] DMA: add help function to check whether dma controller registered

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Date:	Thu, 22 Aug 2013 14:36:53 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Richard Zhao <rizhao@...dia.com>
CC:	linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, vinod.koul@...el.com,
	djbw@...com, grant.likely@...aro.org, rob.herring@...xeda.com,
	devicetree@...r.kernel.org
Subject: Re: [PATCH v2] DMA: add help function to check whether dma controller
 registered

On 08/22/2013 12:43 AM, Richard Zhao wrote:
> DMA client device driver usually needs to know at probe time whether
> dma controller has been registered to deffer probe. So add a help
> function of_dma_check_controller.
> 
> DMA request channel functions can also used to check it, but they
> are usually called at open() time.

This new function is almost identical to the existing
of_dma_request_slave_channel(). Surely the code should be shared?

But that said, I don't see any need for a new function; why can't
drivers simply call of_dma_request_slave_channel() at probe time; from
what I can see, that function doesn't actually request the channel, but
rather simply looks it up, just like this one. The only difference is
that of_dma_xlate() is also called, but that's just doing some data
transformation, not actually recording channel ownership.
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