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

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Date:   Fri, 13 Apr 2018 18:48:43 +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 13 April 2018 at 18:11, 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.
>
> First doesn't it use sound dmaengine library, it should :)

I do not think so. That's the DMA configuration need to set before
audio use it. Not only audio, but also other drivers using DMA need to
configure these configuration what we exported in sprd_dma_config.

>
> Second, I think you should calculate the lengths based on given input. Audio
> is circular buffer so you shall create a circular linked list and submit.
> See how other driver implement circular prepare callback

Yes,  we have not implemented the link list mode for audio now, but in
our plan. So firstly we want to export these necessary configuration
for users to configure.

-- 
Baolin.wang
Best Regards