[PATCH v2 0/1] ASoC: soc-pcm.c: Make sure DAI parameters cleared if the DAI becomes inactive

[Chancel Liu]

It's reasonable that DAI parameters should be cleared if current DAI becomes
inactive.

Only check DAI active status in soc_pcm_hw_free() is not enough since there's
the risk that DAI parameters never be cleared if there're more than one stream
[see A]. Only check DAI active status in soc_pcm_close() is also not enough
since it will cause the cleanup just happening in soc_pcm_close() [see B].

[A] For example, we have stream1 and stream2 for DAI about to stop. stream2
executes soc_pcm_hw_free() before stream1 executes soc_pcm_close(). At the
moment, stream2 should clear current DAI parameters because stream1 passed the
cleanup stage in soc_pcm_hw_free() and stream2 in fact is the only active
stream which has a chance to do clean up. Since DAI active status is not yet
updated by stream1 in soc_pcm_close(), stream2 doesn't know itself should clear
DAI parameters. In result both stream1 and stream2 don't clear the parameters.

[B] Suppose a case: aplay -Dhw:0 44100.wav 48000.wav
In this case, we call soc_pcm_open()->soc_pcm_hw_params()->soc_pcm_hw_free()
->soc_pcm_hw_params()->soc_pcm_hw_free()->soc_pcm_close() in order. The DAI
parameters would be remained in the system even if the playback of 44100.wav is
finished.

In conclusion, it's better to check DAI active status in both soc_pcm_hw_free()
and soc_pcm_close() which makes sure DAI parameters cleared if the DAI becomes
inactive.

changes in v2:
- Patch v1 link: https://lore.kernel.org/all/20230112065834.580192-1-chancel.liu@xxxxxxx/
  Patch v1 tries to introduce a usage count called hw_params_count to fix issue
  on DAI parameters cleanup. However it's not a good fix because not
  considering hw_params() and hw_free() are not symmetrical and hw_params()
  might be called multilpe times by user.
- Both check DAI active status in soc_pcm_hw_free() and soc_pcm_close() which
  makes sure DAI parameters cleared if the DAI becomes inactive.

Chancel Liu (1):
  ASoC: soc-pcm.c: Make sure DAI parameters cleared if the DAI becomes
    inactive

 sound/soc/soc-pcm.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

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2.25.1