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

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Date:   Mon, 16 Apr 2018 14:32:05 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Vinod Koul <vinod.koul@...el.com>
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 16 April 2018 at 11:58, Vinod Koul <vinod.koul@...el.com> wrote:
> On Fri, Apr 13, 2018 at 02:41:48PM +0800, Baolin Wang wrote:
>> On 13 April 2018 at 14:36, Vinod Koul <vinod.koul@...el.com> wrote:
>> > 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...
>>
>> Beside the general configuration, our audio driver will configure the
>> fragment length, block length, maybe transaction length, and they must
>> specify the request type and interrupt type, these are what we want to
>> export for users.
>
> As I said before, you need to derive fragment, block or transaction from

I am sorry I did not make things clear here. What I mean is not only
link list mode(prep_cyclic), but also other modes (prep_slave,
prep_interleaved ...), users still need to configure the fragment
length, block length or transaction length according to their
requirements.

> given prep_cyclic values. Interrupt type needs to be derived with the flags
> passed. Please do see how other drivers make use of it.

Fine. We configure the Interrupt type through the flags passed.

-- 
Baolin.wang
Best Regards