Re: [PATCH v2] ALSA: compress: allow setting codec params after next track

[Takashi Iwai <tiwai@suse.de>]

On Fri, 09 Jun 2023 17:04:16 +0200,
Srinivas Kandagatla wrote:
> 
> For gapless playback it is possible that each track can have different
> codec profile with same decoder, for example we have WMA album,
> we may have different tracks as WMA v9, WMA v10 and so on
> 
> Or if DSP's like QDSP have abililty to switch decoders on single stream
> for each track, then this call could be used to set new codec parameters.
> 
> Existing code does not allow to change this profile while doing gapless
> playback.
> 
> Reuse existing SNDRV_COMPRESS_SET_PARAMS to set this new track params along
> some additional checks to enforce proper state machine.
> 
> With this new changes now the user can call SNDRV_COMPRESS_SET_PARAMS
> anytime after setting next track and additional check in write should
> also ensure that params are set before writing new data.
> 
> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
> ---
> Changes since v1/RFC:
> 	- removed introduction of new IOCTL, as suggested.
> 	- update the state-machine doc.
> 
>  .../sound/designs/compress-offload.rst        | 52 +++++++++----------
>  sound/core/compress_offload.c                 | 10 ++--
>  2 files changed, 33 insertions(+), 29 deletions(-)
> 
> diff --git a/Documentation/sound/designs/compress-offload.rst b/Documentation/sound/designs/compress-offload.rst
> index 935f325dbc77..205cadcabe70 100644
> --- a/Documentation/sound/designs/compress-offload.rst
> +++ b/Documentation/sound/designs/compress-offload.rst
> @@ -256,32 +256,32 @@ Gapless Playback SM
>  For Gapless, we move from running state to partial drain and back, along
>  with setting of meta_data and signalling for next track ::
>  
> -
> -                                        +----------+
> -                compr_drain_notify()    |          |
> -              +------------------------>|  RUNNING |
> -              |                         |          |
> -              |                         +----------+
> -              |                              |
> -              |                              |
> -              |                              | compr_next_track()
> -              |                              |
> -              |                              V
> -              |                         +----------+
> -              |                         |          |
> -              |                         |NEXT_TRACK|
> -              |                         |          |
> -              |                         +----------+
> -              |                              |
> -              |                              |
> -              |                              | compr_partial_drain()
> -              |                              |
> -              |                              V
> -              |                         +----------+
> -              |                         |          |
> -              +------------------------ | PARTIAL_ |
> -                                        |  DRAIN   |
> -                                        +----------+
> +                            +----------+
> +     compr_drain_notify()   |          | compr_set_params() iff next-track set.
> +  +------------------------>|  RUNNING |----------------------+
> +  |                         |          |                      |
> +  |                         +----------+                      |
> +  |                              |                            |
> +  |                              |                            |
> +  |                              | compr_next_track()         |
> +  |                              |                            V
> +  |                              V                            |
> +  |                         +----------+                      |
> +  |                         |          |                      |
> +  |                         |NEXT_TRACK|                      |
> +  |                         |          |                      |
> +  |                         +----------+                      |
> +  |                              |                            |
> +  |                              +----------------------------+
> +  |                              |
> +  |                              | compr_partial_drain()
> +  |                              |
> +  |                              V
> +  |                         +----------+
> +  |                         |          |
> +  +------------------------ | PARTIAL_ |
> +                            |  DRAIN   |
> +                            +----------+
>  
>  Not supported
>  =============
> diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c
> index 243acad89fd3..fe67228e74b3 100644
> --- a/sound/core/compress_offload.c
> +++ b/sound/core/compress_offload.c
> @@ -294,6 +294,9 @@ static ssize_t snd_compr_write(struct file *f, const char __user *buf,
>  	case SNDRV_PCM_STATE_SETUP:
>  	case SNDRV_PCM_STATE_PREPARED:
>  	case SNDRV_PCM_STATE_RUNNING:
> +		/* Make sure next track params are set before writing new data */
> +		if (stream->next_track)
> +			return -EPERM;

Hm, does this logic correctly match with the comment above?
Also, this misses the mutex unlock.


thanks,

Takashi