linux-kernel - [PATCH RFC] ASoC: dai playback_active and capture

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Message-Id: <20180419140612.11049-1-jbrunet@baylibre.com>
Date:   Thu, 19 Apr 2018 16:06:12 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>
Cc:     Jerome Brunet <jbrunet@...libre.com>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, Kevin Hilman <khilman@...libre.com>
Subject: [PATCH RFC] ASoC: dai playback_active and capture_active may be greater than 1

At the moment playback_active and capture_active are using only 1 bit so
the maximum active count is 1.

However, snd_soc_runtime_activate() may be called several time on the
same dai. This happens when a dai is part of several dai_links. It is
often the case for "snd-soc-dummy-dai".

This is a problem if snd_soc_runtime_activate() is called an even number
of times on a dai. In this case the active count overflow back to 0. As
consequence, ASoC functions, such as soc_dpcm_runtime_update(), won't run
correctly.

Storing these usage counts on plain 'unsigned int' solves the problem.

Fixes: f0fba2ad1b6b ("ASoC: multi-component - ASoC Multi-Component Support")
Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
---

Hi,

I found this problem while working on ASoC support for a new platform.
During a playback, using DPCM, if I changed the backend dai, nothing
happened, old backend path was not pruned, new backend path was not added.

Here is how it goes:
1 FE and 2 BE, all 3 using snd-soc-dummy-dai for the codec_dai (ATM).

On playback start:
 - BE #1 activates and increments snd-soc-dummy-dai's playback_active
 - FE activates and increments snd-soc-dummy-dai's playback_active

The playback works but snd-soc-dummy-dai's playback_active value is now 0.

Through a mux kcontrol, change BE client of FE, from BE #1 to BE #2.
 -> trigger soc_dpcm_runtime_update().
    -> checks fe's codec_dai playback_active which is zero so playback
    path processing is skipped, keeping the old invalid path.

 include/sound/soc-dai.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/sound/soc-dai.h b/include/sound/soc-dai.h
index 8ad11669e4d8..35ebb0be5114 100644
--- a/include/sound/soc-dai.h
+++ b/include/sound/soc-dai.h
@@ -294,8 +294,8 @@ struct snd_soc_dai {
 	struct snd_soc_dai_driver *driver;

 	/* DAI runtime info */
-	unsigned int capture_active:1;		/* stream is in use */
-	unsigned int playback_active:1;		/* stream is in use */
+	unsigned int capture_active;		/* stream usage count */
+	unsigned int playback_active;		/* stream usage count */
 	unsigned int probed:1;

 	unsigned int active;
-- 
2.14.3