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

Priit Laes
2016-11-03T08:42:59Z

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-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> Signed-off-by: Chen-Yu Tsai <wens-jdAy2FN1RRM@public.gmane.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
>

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