linux-kernel - Re: [PATCH] ASoC: fsl_esai: Add spin lock to protect reset and stop

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Date:   Wed, 23 Oct 2019 11:31:03 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Shengjiu Wang <shengjiu.wang@....com>
Cc:     timur@...nel.org, Xiubo.Lee@...il.com, festevam@...il.com,
        broonie@...nel.org, alsa-devel@...a-project.org,
        lgirdwood@...il.com, perex@...ex.cz, tiwai@...e.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ASoC: fsl_esai: Add spin lock to protect reset and stop

On Wed, Oct 23, 2019 at 03:29:49PM +0800, Shengjiu Wang wrote:
> xrun may happen at the end of stream, the
> trigger->fsl_esai_trigger_stop maybe called in the middle of
> fsl_esai_hw_reset, this may cause esai in wrong state
> after stop, and there may be endless xrun interrupt.

What about fsl_esai_trigger_start? It touches ESAI_xFCR_xFEN bit
that is being checked in the beginning of fsl_esai_hw_reset.

Could the scenario below be possible also?

1) ESAI TX starts
2) Xrun happens to TX
3) Starting fsl_esai_hw_reset (enabled[TX] = true; enabled[RX] = false)
4) ESAI RX starts
5) Finishing fsl_esai_hw_reset (enabled[RX] is still false)

Thanks
Nicolin

> So Add spin lock to lock these two function.
> 
> Fixes: 7ccafa2b3879 ("ASoC: fsl_esai: recover the channel swap after xrun")
> Signed-off-by: Shengjiu Wang <shengjiu.wang@....com>
> ---
>  sound/soc/fsl/fsl_esai.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/sound/soc/fsl/fsl_esai.c b/sound/soc/fsl/fsl_esai.c
> index 37b14c48b537..6a797648b66d 100644
> --- a/sound/soc/fsl/fsl_esai.c
> +++ b/sound/soc/fsl/fsl_esai.c
> @@ -33,6 +33,7 @@
>   * @fsysclk: system clock source to derive HCK, SCK and FS
>   * @spbaclk: SPBA clock (optional, depending on SoC design)
>   * @task: tasklet to handle the reset operation
> + * @lock: spin lock to handle reset and stop behavior
>   * @fifo_depth: depth of tx/rx FIFO
>   * @slot_width: width of each DAI slot
>   * @slots: number of slots
> @@ -56,6 +57,7 @@ struct fsl_esai {
>  	struct clk *fsysclk;
>  	struct clk *spbaclk;
>  	struct tasklet_struct task;
> +	spinlock_t lock; /* Protect reset and stop */
>  	u32 fifo_depth;
>  	u32 slot_width;
>  	u32 slots;
> @@ -676,8 +678,10 @@ static void fsl_esai_hw_reset(unsigned long arg)
>  {
>  	struct fsl_esai *esai_priv = (struct fsl_esai *)arg;
>  	bool tx = true, rx = false, enabled[2];
> +	unsigned long lock_flags;
>  	u32 tfcr, rfcr;
>  
> +	spin_lock_irqsave(&esai_priv->lock, lock_flags);
>  	/* Save the registers */
>  	regmap_read(esai_priv->regmap, REG_ESAI_TFCR, &tfcr);
>  	regmap_read(esai_priv->regmap, REG_ESAI_RFCR, &rfcr);
> @@ -715,6 +719,8 @@ static void fsl_esai_hw_reset(unsigned long arg)
>  		fsl_esai_trigger_start(esai_priv, tx);
>  	if (enabled[rx])
>  		fsl_esai_trigger_start(esai_priv, rx);
> +
> +	spin_unlock_irqrestore(&esai_priv->lock, lock_flags);
>  }
>  
>  static int fsl_esai_trigger(struct snd_pcm_substream *substream, int cmd,
> @@ -722,6 +728,7 @@ static int fsl_esai_trigger(struct snd_pcm_substream *substream, int cmd,
>  {
>  	struct fsl_esai *esai_priv = snd_soc_dai_get_drvdata(dai);
>  	bool tx = substream->stream == SNDRV_PCM_STREAM_PLAYBACK;
> +	unsigned long lock_flags;
>  
>  	esai_priv->channels[tx] = substream->runtime->channels;
>  
> @@ -734,7 +741,9 @@ static int fsl_esai_trigger(struct snd_pcm_substream *substream, int cmd,
>  	case SNDRV_PCM_TRIGGER_SUSPEND:
>  	case SNDRV_PCM_TRIGGER_STOP:
>  	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
> +		spin_lock_irqsave(&esai_priv->lock, lock_flags);
>  		fsl_esai_trigger_stop(esai_priv, tx);
> +		spin_unlock_irqrestore(&esai_priv->lock, lock_flags);
>  		break;
>  	default:
>  		return -EINVAL;
> @@ -1002,6 +1011,7 @@ static int fsl_esai_probe(struct platform_device *pdev)
>  
>  	dev_set_drvdata(&pdev->dev, esai_priv);
>  
> +	spin_lock_init(&esai_priv->lock);
>  	ret = fsl_esai_hw_init(esai_priv);
>  	if (ret)
>  		return ret;
> -- 
> 2.21.0
>