[PATCH] ASoC: mediatek: Increase periods_min in capture

[koro.chen@mediatek.com (Koro Chen)]

Any suggestion for this patch?

On Mon, 2015-09-14 at 14:51 +0800, Koro Chen wrote:
> In capture, there is chance that hw_ptr reported at IRQ is
> a little smaller than period_size due to internal AFE buffer.
> In the case of ping-pong buffer:
> 
> |xxxxxxxxxxxxxxxxxxxxxxxxxxxx--|-----------------------------|
>                             hw_ptr < period_size
> 
> This available buffer will not be read since its size is smaller than
> avail_min (which is period_size by default), and read thread continues
> to sleep. If the next hw_ptr is just a little larger than buffer_size,
> overrun occurs. One more period can hold the possible unread buffer.
> 
> Signed-off-by: Koro Chen <koro.chen@mediatek.com>
> ---
>  sound/soc/mediatek/mtk-afe-pcm.c |   17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/sound/soc/mediatek/mtk-afe-pcm.c b/sound/soc/mediatek/mtk-afe-pcm.c
> index d190fe0..f5baf3c 100644
> --- a/sound/soc/mediatek/mtk-afe-pcm.c
> +++ b/sound/soc/mediatek/mtk-afe-pcm.c
> @@ -549,6 +549,23 @@ static int mtk_afe_dais_startup(struct snd_pcm_substream *substream,
>  	memif->substream = substream;
>  
>  	snd_soc_set_runtime_hwparams(substream, &mtk_afe_hardware);
> +
> +	/*
> +	 * Capture cannot use ping-pong buffer since hw_ptr at IRQ may be
> +	 * smaller than period_size due to AFE's internal buffer.
> +	 * This easily leads to overrun when avail_min is period_size.
> +	 * One more period can hold the possible unread buffer.
> +	 */
> +	if (substream->stream == SNDRV_PCM_STREAM_CAPTURE) {
> +		ret = snd_pcm_hw_constraint_minmax(runtime,
> +						   SNDRV_PCM_HW_PARAM_PERIODS,
> +						   3,
> +						   mtk_afe_hardware.periods_max);
> +		if (ret < 0) {
> +			dev_err(afe->dev, "hw_constraint_minmax failed\n");
> +			return ret;
> +		}
> +	}
>  	ret = snd_pcm_hw_constraint_integer(runtime,
>  					    SNDRV_PCM_HW_PARAM_PERIODS);
>  	if (ret < 0)