linux-kernel - Re: [PATCH v2 2/6] ASoC: dwc: Ensure FIFOs are flushed to prevent channel swap

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Date:	Fri, 12 Dec 2014 10:37:34 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Andrew Jackson <andrew.jackson@....com>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.de>
CC:	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Rajeev Kumar <rajeevkumar.linux@...il.com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/6] ASoC: dwc: Ensure FIFOs are flushed to prevent
 channel swap

On 12/12/2014 10:25 AM, Andrew Jackson wrote:
> From: Andrew Jackson <Andrew.Jackson@....com>
>
> If the FIFOs aren't flushed, the left/right channels may be swapped:
> this may occur if the FIFOs are not empty when the streams start.
>
> Signed-off-by: Andrew Jackson <Andrew.Jackson@....com>
> ---
>   sound/soc/dwc/designware_i2s.c |    2 ++
>   1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/sound/soc/dwc/designware_i2s.c b/sound/soc/dwc/designware_i2s.c
> index ef771ea..b9d6a25 100644
> --- a/sound/soc/dwc/designware_i2s.c
> +++ b/sound/soc/dwc/designware_i2s.c
> @@ -228,12 +228,14 @@ static int dw_i2s_hw_params(struct snd_pcm_substream *substream,
>   	i2s_disable_channels(dev, substream->stream);
>
>   	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
> +		i2s_write_reg(dev->i2s_base, TXFFR, 1);
>   		i2s_write_reg(dev->i2s_base, TCR(ch_reg), xfer_resolution);
>   		i2s_write_reg(dev->i2s_base, TFCR(ch_reg), 0x02);
>   		irq = i2s_read_reg(dev->i2s_base, IMR(ch_reg));
>   		i2s_write_reg(dev->i2s_base, IMR(ch_reg), irq & ~0x30);
>   		i2s_write_reg(dev->i2s_base, TER(ch_reg), 1);
>   	} else {
> +		i2s_write_reg(dev->i2s_base, RXFFR, 1);
>   		i2s_write_reg(dev->i2s_base, RCR(ch_reg), xfer_resolution);
>   		i2s_write_reg(dev->i2s_base, RFCR(ch_reg), 0x07);
>   		irq = i2s_read_reg(dev->i2s_base, IMR(ch_reg));
>

This should probably go into the prepare callback. prepare is for example 
also called when recovering from a underrun/overrun. Whereas hwparams is 
only called during initial setup of the stream.
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