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

[Priit Laes]

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
> 
> Â* @src_maxburst: the maximum number of words (note: words, as in
> Â* units of the src_addr_width member, not bytes) that can be sent
> Â* in one burst to the device. Typically something like half the
> Â* FIFO depth on I/O peripherals so you don't overflow it. This
> Â* may or may not be applicable on memory sources.
> Â* @dst_maxburst: same as src_maxburst but for destination target

> Â* 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@xxxxxxxxx>
> Signed-off-by: Chen-Yu Tsai <wens@xxxxxxxx>
> ---
> Âsound/soc/sunxi/sun4i-codec.c | 4 ++--
> Â1 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)
> Â
> Â	/* DMA configuration for TX FIFO */
> Â	scodec->playback_dma_data.addr = res->start + quirks-
> >reg_dac_txdata;
> -	scodec->playback_dma_data.maxburst = 4;
> +	scodec->playback_dma_data.maxburst = 8;
> Â	scodec->playback_dma_data.addr_width =
> DMA_SLAVE_BUSWIDTH_2_BYTES;
> Â
> Â	/* DMA configuration for RX FIFO */
> Â	scodec->capture_dma_data.addr = res->start + quirks-
> >reg_adc_rxdata;
> -	scodec->capture_dma_data.maxburst = 4;
> +	scodec->capture_dma_data.maxburst = 8;
> Â	scodec->capture_dma_data.addr_width =
> DMA_SLAVE_BUSWIDTH_2_BYTES;
> Â
> Â	ret = snd_soc_register_codec(&pdev->dev, quirks->codec,
> --Â
> 2.10.2
>