[alsa-devel] [PATCH - DMA engine v2 1/1] ALSA: SOC: DMA: increment buffer pointer atomically

[Timo Wischer]

Hi all,

Any comments to the patch in [1]?

Should I change anything?

[1] 
http://mailman.alsa-project.org/pipermail/alsa-devel/2018-July/138319.html

Best regards

*Timo Wischer*

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On 07/19/2018 12:29 PM, twischer at de.adit-jv.com wrote:
> From: Andreas Pape <apape at de.adit-jv.com>
>
> Setting pointer and afterwards check for wrap around leads
> to the possibility of returning the inconsistent pointer position.
> This patch increments buffer pointer atomically to avoid this issue.
>
> Signed-off-by: Andreas Pape <apape at de.adit-jv.com>
>
> Since commit: b7ae6f3 dmaengine implementation has been moved
> from ASoC to ALSA core. So change goes to sound/soc/soc-dmaengine-pcm.c,
> apply to sound/core/pcm_dmaengine.c now
>
> cherry picked from ADIT v3.14 e2f803f("ALSA: SOC: DMA: increment buffer pointer atomically")
> Signed-off-by: Veeraiyan Chidambaram <veeraiyan.chidambaram at in.bosch.com>
> (cherry picked from ADIT v4.1 commit 9e7eff10a38157db75f12e032fc378d3104a2812)
> Signed-off-by: Takashi Sakamoto <takashi.sakamoto at miraclelinux.com>
> (cherry picked from ADIT v4.9 commit 66c00aa1e7cd3b077fc2e5a45a4594b86246cf78)
> Signed-off-by: Jiada Wang <jiada_wang at mentor.com>
>
> Signed-off-by: Timo Wischer <twischer at de.adit-jv.com>
> ---
>
> v1 can be found in
> http://mailman.alsa-project.org/pipermail/alsa-devel/2016-November/115277.html
>
> diff --git a/sound/core/pcm_dmaengine.c b/sound/core/pcm_dmaengine.c
> index 8eb58c7..0a7ed85 100644
> --- a/sound/core/pcm_dmaengine.c
> +++ b/sound/core/pcm_dmaengine.c
> @@ -139,12 +139,14 @@ EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_set_config_from_dai_data);
>   
>   static void dmaengine_pcm_dma_complete(void *arg)
>   {
> +	unsigned int new_pos;
>   	struct snd_pcm_substream *substream = arg;
>   	struct dmaengine_pcm_runtime_data *prtd = substream_to_prtd(substream);
>   
> -	prtd->pos += snd_pcm_lib_period_bytes(substream);
> -	if (prtd->pos >= snd_pcm_lib_buffer_bytes(substream))
> -		prtd->pos = 0;
> +	new_pos = READ_ONCE(prtd->pos) + snd_pcm_lib_period_bytes(substream);
> +	if (new_pos >= snd_pcm_lib_buffer_bytes(substream))
> +		new_pos = 0;
> +	WRITE_ONCE(prtd->pos, new_pos);
>   
>   	snd_pcm_period_elapsed(substream);
>   }
> @@ -235,7 +237,7 @@ EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_trigger);
>   snd_pcm_uframes_t snd_dmaengine_pcm_pointer_no_residue(struct snd_pcm_substream *substream)
>   {
>   	struct dmaengine_pcm_runtime_data *prtd = substream_to_prtd(substream);
> -	return bytes_to_frames(substream->runtime, prtd->pos);
> +	return bytes_to_frames(substream->runtime, READ_ONCE(prtd->pos));
>   }
>   EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_pointer_no_residue);
>