linux-kernel - Re: [linux-sunxi] [PATCH v2 04/14] ASoC: sun4i-codec: Increase DMA max burst to 8

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Date:   Thu, 03 Nov 2016 10:42:59 +0200
From:   Priit Laes <plaes@...es.org>
To:     wens@...e.org, Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     alsa-devel@...a-project.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-sunxi@...glegroups.com, Vinod Koul <vinod.koul@...el.com>
Subject: Re: [linux-sunxi] [PATCH v2 04/14] ASoC: sun4i-codec: Increase DMA
 max burst to 8

On Thu, 2016-11-03 at 15:55 +0800, Chen-Yu Tsai wrote:
> According to the DMA engine API documentation, maxburst denotes the
> largest possible size of a single transfer, so as not to overflow
> destination FIFOs as explained in this excerpt from dmaengine.h
> 
>  * @src_maxburst: the maximum number of words (note: words, as in
>  * units of the src_addr_width member, not bytes) that can be sent
>  * in one burst to the device. Typically something like half the
>  * FIFO depth on I/O peripherals so you don't overflow it. This
>  * may or may not be applicable on memory sources.
>  * @dst_maxburst: same as src_maxburst but for destination target

>  * mutatis mutandis.

^^ :)

> 
> The TX FIFO is 64 samples deep for stereo, and the RX FIFO is 16
> samples deep. So maxburst could be 32 and 8 for TX and RX
> respectively.
> 
> Unfortunately the sunxi DMA controller driver takes maxburst as
> the requested burst size, rather than a limit, and returns an error
> for unsupported values. The original value was 4, but some later
> SoCs do not officially support this burst size.
> 
> This patch increases maxburst on the TX side to 8, which is supported
> by all variants of the sunxi DMA controller.
> 
> Cc: Vinod Koul <vinod.koul@...el.com>
> Signed-off-by: Chen-Yu Tsai <wens@...e.org>
> ---
>  sound/soc/sunxi/sun4i-codec.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/soc/sunxi/sun4i-codec.c b/sound/soc/sunxi/sun4i-
> codec.c
> index 61ae502a5061..d867b96d367b 100644
> --- a/sound/soc/sunxi/sun4i-codec.c
> +++ b/sound/soc/sunxi/sun4i-codec.c
> @@ -886,12 +886,12 @@ static int sun4i_codec_probe(struct
> platform_device *pdev)
>  
>  	/* DMA configuration for TX FIFO */
>  	scodec->playback_dma_data.addr = res->start + quirks-
> >reg_dac_txdata;
> -	scodec->playback_dma_data.maxburst = 4;
> +	scodec->playback_dma_data.maxburst = 8;
>  	scodec->playback_dma_data.addr_width =
> DMA_SLAVE_BUSWIDTH_2_BYTES;
>  
>  	/* DMA configuration for RX FIFO */
>  	scodec->capture_dma_data.addr = res->start + quirks-
> >reg_adc_rxdata;
> -	scodec->capture_dma_data.maxburst = 4;
> +	scodec->capture_dma_data.maxburst = 8;
>  	scodec->capture_dma_data.addr_width =
> DMA_SLAVE_BUSWIDTH_2_BYTES;
>  
>  	ret = snd_soc_register_codec(&pdev->dev, quirks->codec,
> -- 
> 2.10.2
>