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

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Date:   Thu, 2 May 2019 11:34:46 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Sameer Pujar <spujar@...dia.com>
Cc:     dan.j.williams@...el.com, tiwai@...e.com, jonathanh@...dia.com,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [RFC] dmaengine: add fifo_size member

On 30-04-19, 17:00, Sameer Pujar wrote:
> During the DMA transfers from memory to I/O, it was observed that transfers
> were inconsistent and resulted in glitches for audio playback. It happened
> because fifo size on DMA did not match with slave channel configuration.
> 
> currently 'dma_slave_config' structure does not have a field for fifo size.
> Hence the platform pcm driver cannot pass the fifo size as a slave_config.
> Note that 'snd_dmaengine_dai_dma_data' structure has fifo_size field which
> cannot be used to pass the size info. This patch introduces fifo_size field
> and the same can be populated on slave side. Users can set required size
> for slave peripheral (multiple channels can be independently running with
> different fifo sizes) and the corresponding sizes are programmed through
> dma_slave_config on DMA side.

FIFO size is a hardware property not sure why you would want an
interface to program that?

On mismatch, I guess you need to take care of src/dst_maxburst..

> 
> Request for feedback/suggestions.
> 
> Signed-off-by: Sameer Pujar <spujar@...dia.com>
> ---
>  include/linux/dmaengine.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index d49ec5c..9ec198b 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -351,6 +351,8 @@ enum dma_slave_buswidth {
>   * @slave_id: Slave requester id. Only valid for slave channels. The dma
>   * slave peripheral will have unique id as dma requester which need to be
>   * pass as slave config.
> + * @fifo_size: Fifo size value. The dma slave peripheral can configure required
> + * fifo size and the same needs to be passed as slave config.
>   *
>   * This struct is passed in as configuration data to a DMA engine
>   * in order to set up a certain channel for DMA transport at runtime.
> @@ -376,6 +378,7 @@ struct dma_slave_config {
>  	u32 dst_port_window_size;
>  	bool device_fc;
>  	unsigned int slave_id;
> +	u32 fifo_size;
>  };
>  
>  /**
> -- 
> 2.7.4

-- 
~Vinod