[alsa-devel] [PATCH 1/4] ALSA: hda: Make sure DMA is stopped by reading back the RUN bit

[Takashi Iwai]

On Tue, 15 May 2018 08:40:53 +0200,
Sriram Periyasamy wrote:
> 
> From: Pardha Saradhi K <pardha.saradhi.kesapragada at intel.com>
> 
> As per HW recommendation, after clearing the RUN bit,
> software must read a 0 from the RUN bit, before modifying
> related control registers or re-starting the DMA engine.

This is already done in snd_hdac_stream_sync().

Doing this in snd_hdac_stream_clear() may delay the sync'ed operations
unnecessarily.


thanks,

Takashi

> 
> Signed-off-by: Pardha Saradhi K <pardha.saradhi.kesapragada at intel.com>
> Signed-off-by: Sriram Periyasamy <sriramx.periyasamy at intel.com>
> ---
>  sound/hda/hdac_stream.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/sound/hda/hdac_stream.c b/sound/hda/hdac_stream.c
> index e1472c7ab6c1..2000ea6f48fa 100644
> --- a/sound/hda/hdac_stream.c
> +++ b/sound/hda/hdac_stream.c
> @@ -70,8 +70,23 @@ EXPORT_SYMBOL_GPL(snd_hdac_stream_start);
>   */
>  void snd_hdac_stream_clear(struct hdac_stream *azx_dev)
>  {
> +	int timeout = 300;
> +	unsigned char val;
> +
>  	snd_hdac_stream_updateb(azx_dev, SD_CTL,
>  				SD_CTL_DMA_START | SD_INT_MASK, 0);
> +
> +	do {
> +		udelay(3);
> +		val = snd_hdac_stream_readb(azx_dev, SD_CTL) &
> +				SD_CTL_DMA_START;
> +		if (!val)
> +			break;
> +	} while (--timeout);
> +
> +	if (!timeout)
> +		dev_err(azx_dev->bus->dev, "unable to stop the stream\n");
> +
>  	snd_hdac_stream_writeb(azx_dev, SD_STS, SD_INT_MASK); /* to be sure */
>  	azx_dev->running = false;
>  }
> -- 
> 2.7.4
>