linux-kernel - Re: [PATCH 4/5] dmaengine: sprd: Add Spreadtrum DMA configuration

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Date:   Fri, 13 Apr 2018 12:06:42 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Eric Long <eric.long@...eadtrum.com>,
        Mark Brown <broonie@...nel.org>, dmaengine@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/5] dmaengine: sprd: Add Spreadtrum DMA configuration

On Fri, Apr 13, 2018 at 02:17:34PM +0800, Baolin Wang wrote:

> > Agreed, users only care about grabbing a channel, setting a descriptor and
> > submitting that.
> >
> > I think you need to go back and think about this a bit, please do go thru
> > dmaengine documentation and see other driver examples.
> >
> > We don't typically expose these to users, they give us a transfer and we set
> > that up in hardware for efficient. Its DMA so people expect us to use fastest
> > mechanism available.
> 
> But there are some configuration are really special for Spreadtrum
> DMA, and must need user to specify how to configure, especially some
> scenarios of audio. So I wander if we can add one pointer for
> 'dma_slave_config' to expand some special DMA configuration
> requirements, like:
> 
> struct dma_slave_config {
>     ......
>     unsigned int slave_id;
>     void *platform_data;
> };
> 
> So if some DMA has some special configuration (such as Spreadtrum
> DMA), they can user this platform_data pointer. Like xilinx DMA, they
> also have some special configuration.

Well we all think our HW is special and needs some additional stuff, most of
the cases turns out not to be the case.

Can you explain how audio in this case additional configuration...

-- 
~Vinod