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

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

[twischer]

From: Andreas Pape <apape@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@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@in.bosch.com>
(cherry picked from ADIT v4.1 commit 9e7eff10a38157db75f12e032fc378d3104a2812)
Signed-off-by: Takashi Sakamoto <takashi.sakamoto@miraclelinux.com>
(cherry picked from ADIT v4.9 commit 66c00aa1e7cd3b077fc2e5a45a4594b86246cf78)
Signed-off-by: Jiada Wang <jiada_wang@mentor.com>

Signed-off-by: Timo Wischer <twischer@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);
 
-- 
2.7.4

Re: [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*

*A*dvanced *D*river *I*nformation *T*echnology GmbH
Engineering Software Base (ADITG/ESB)
Robert-Bosch-Str. 200
31139 Hildesheim
Germany

Tel. +49 5121 49 6938
Fax +49 5121 49 6999
twischer@de.adit-jv.com

ADIT is a joint venture company of Robert Bosch GmbH/Robert Bosch Car 
Multimedia GmbH and DENSO Corporation
Sitz: Hildesheim, Registergericht: Amtsgericht Hildesheim HRB 3438
Geschäftsführung: Wilhelm Grabow, Ken Yaguchi


On 07/19/2018 12:29 PM, twischer@de.adit-jv.com wrote:
> From: Andreas Pape <apape@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@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@in.bosch.com>
> (cherry picked from ADIT v4.1 commit 9e7eff10a38157db75f12e032fc378d3104a2812)
> Signed-off-by: Takashi Sakamoto <takashi.sakamoto@miraclelinux.com>
> (cherry picked from ADIT v4.9 commit 66c00aa1e7cd3b077fc2e5a45a4594b86246cf78)
> Signed-off-by: Jiada Wang <jiada_wang@mentor.com>
>
> Signed-off-by: Timo Wischer <twischer@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);
>   

_______________________________________________
Alsa-devel mailing list
Alsa-devel@alsa-project.org
http://mailman.alsa-project.org/mailman/listinfo/alsa-devel