linux-kernel - Re: [PATCH] [RFC] dmaengine: add fifo

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Date:   Tue, 23 Jul 2019 11:24:14 +0530
From:   Sameer Pujar <spujar@...dia.com>
To:     Vinod Koul <vkoul@...nel.org>,
        Peter Ujfalusi <peter.ujfalusi@...com>
CC:     <dan.j.williams@...el.com>, <tiwai@...e.com>,
        <jonathanh@...dia.com>, <dmaengine@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <sharadg@...dia.com>,
        <rlokhande@...dia.com>, <dramesh@...dia.com>, <mkumard@...dia.com>
Subject: Re: [PATCH] [RFC] dmaengine: add fifo_size member


On 7/19/2019 10:34 AM, Vinod Koul wrote:
> On 05-07-19, 11:45, Sameer Pujar wrote:
>> Hi Vinod,
>>
>> What are your final thoughts regarding this?
> Hi sameer,
>
> Sorry for the delay in replying
>
> On this, I am inclined to think that dma driver should not be involved.
> The ADMAIF needs this configuration and we should take the path of
> dma_router for this piece and add features like this to it

Hi Vinod,

The configuration is needed by both ADMA and ADMAIF. The size is 
configurable
on ADMAIF side. ADMA needs to know this info and program accordingly.
Not sure if dma_router can help to achieve this.

I checked on dma_router. It would have been useful when a configuration 
exported
via ADMA, had to be applied to ADMAIF. Please correct me if I am wrong here.

>> Thanks,
>> Sameer.
>>
>>>> Where does ADMAIF driver reside in kernel, who configures it for normal
>>>> dma txns..?
>>> Not yet, we are in the process of upstreaming ADMAIF driver.
>>> To describe briefly, audio subsystem is using ALSA SoC(ASoC) layer.
>>> ADMAIF is
>>> registered as platform driver and exports DMA functionality. It
>>> registers PCM
>>> devices for each Rx/Tx ADMAIF channel. During PCM playback/capture
>>> operations,
>>> ALSA callbacks configure DMA channel using API dmaengine_slave_config().
>>> RFC patch proposed, is to help populate FIFO_SIZE value as well during
>>> above
>>> call, since ADMA requires it.
>>>> Also it wold have helped the long discussion if that part was made clear
>>>> rather than talking about peripheral all this time :(
>>> Thought it was clear, though should have avoided using 'peripheral' in
>>> the
>>> discussions. Sorry for the confusion.