linux-kernel - Re: [PATCH, RFC] MIPS: jz4740: use dma filter function

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Message-ID: <54ABDA66.7040002@metafoo.de>
Date:	Tue, 06 Jan 2015 13:51:50 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Måns Rullgård <mans@...sr.com>
CC:	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	Ralf Baechle <ralf@...ux-mips.org>, dmaengine@...r.kernel.org,
	alsa-devel@...a-project.org, linux-mmc@...r.kernel.org,
	linux-mips@...ux-mips.org
Subject: Re: [PATCH, RFC] MIPS: jz4740: use dma filter function

On 01/06/2015 01:47 PM, Måns Rullgård wrote:
> Lars-Peter Clausen <lars@...afoo.de> writes:
>
>> On 01/05/2015 11:39 PM, Arnd Bergmann wrote:
>>> As discussed on the topic of shmobile DMA today, jz4740 is the only
>>> user of the slave_id field in dma_slave_config besides shmobile. This
>>> use is really incompatible with the way that other drivers use the
>>> dmaengine API, so we should get rid of it.
>>
>> Do you have a link to that discussion?
>>
>>>
>>> This adds a trivial filter function that uses the filter param to
>>> pass the dma type, and uses that in both drivers.
>>
>> In my opinion that's just from bad to worse. Using filter functions
>> isn't that great in the first place. And using them to pass data from
>> the consumer to the DMA provider is just a horrible abuse of the API.
>
> It seems to me the only sane way to use the dmaengine API is in
> conjunction with DT.

At the moment yes. For non DT we need something like the gpiod lookup tables 
that allow you to specify the assignment of the DMA channel in the machine 
driver.

- Lars


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