linux-kernel - Re: dmaengine: dw-dmac: Custom cyclic API (Why?)

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Message-ID: <20170102101802.GX3573@localhost>
Date:   Mon, 2 Jan 2017 15:48:03 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Jose Abreu <Jose.Abreu@...opsys.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        vireshk@...nel.org
Subject: Re: dmaengine: dw-dmac: Custom cyclic API (Why?)

On Mon, Jan 02, 2017 at 10:38:00AM +0200, Andy Shevchenko wrote:
> On Fri, 2016-12-30 at 12:05 +0000, Jose Abreu wrote:
> > ++dw-dmac Maintainers
> > 
> > 
> > On 30-12-2016 11:32, Jose Abreu wrote:
> > > Hi All,
> > > 
> > > 
> > > I am going to work with dw-dmac AHB controller and I wanted to
> > > use SND_DMAENGINE_PCM. In order to use this, a standard DMA
> > > driver with cyclic support is needed. I found out that dw-dmac is
> > > capable of cyclic transfers but instead of using the DMA engine
> > > standard cyclic API it uses a custom API. Is there any specific
> > > reason for this? What is the effort to change the custom API to a
> > > standard DMA engine cyclic API?
> > > 
> 
> Because it was a predecessor of generic implementation.

And we don't have an implementation that uses this.

> I used to have some semi-finished patch to switch to generic API, though
> at that point I had no means to test it.
> 
> Since I eventually got iDMA 32-bit, which is used as LPE Audio DMA
> engine, support in my branch I might test it in the future, though I
> think someone else would be much faster than me.

no we can't, since the DSP is involved and takes control, so unless we do
lots of nasty hacks, it won't be testable. I don't see the ROI for such an
effort.

not sure about non intel ones, viresh?

btw, feel free to test and send patches if you have such a h/w

-- 
~Vinod