[RFC PATCH] ALSA: compress: add support to change codec profile in gapless playback

[Pierre-Louis Bossart]

On 7/2/20 6:11 AM, Srinivas Kandagatla wrote:
> For gapless playback its 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
> 
> Existing code does not allow to change this profile while doing gapless
> playback.
> 
> This patch adds new SNDRV_COMPRESS_SET_CODEC_PARAMS IOCTL to allow
> userspace to set this new parameters required for new codec profile.

That does not seem fully correct to me. WMA profiles are actually 
different encoding schemes - specifically the WMA 10 LBR.

The premise for gapless playback was that the same codec and profile be 
used between tracks, so that the same internal delay was used. If you 
look at the output data, it's made of zeroes for N samples, and then you 
see decoded data. When you change tracks, the first N samples actually 
come from the previous track.

If you change coding schemes between tracks, you cannot call this 
gapless playback. You will both remove the last N samples of the 
previous track and insert M zeroes (for the new decoder).

If you wanted to support such a mode, you would need to provide an 
indication of the delay difference, e.g. by looking at the ID3 tags and 
let firmware realign. Unfortunately, you don't send this information 
with the new IOCTL? You would also need firmware tricks for the first 
decoder to flush out its output and the new decoder to realign.

I also don't see how one might end-up with different profiles for an 
album in the first place. The gapless use came mostly from ripping live 
music recorded on audio CDs in different tracks, and it would have taken 
a twisted mind to select different encodings between tracks.

If the 'album' is really a playlist, then the gapless playback as 
supported by the ASoC compressed layer is nearly useless. What you would 
really want is cross-fade but that's a different use case and 
implementation that would be needed.

> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla at linaro.org>
> ---
>   include/sound/compress_driver.h       |  5 +++
>   include/sound/soc-component.h         |  3 ++
>   include/sound/soc-dai.h               |  5 +++
>   include/uapi/sound/compress_offload.h |  1 +
>   sound/core/compress_offload.c         | 54 ++++++++++++++++++++++++---
>   sound/soc/soc-compress.c              | 30 +++++++++++++++
>   sound/soc/soc-dai.c                   | 14 +++++++
>   7 files changed, 106 insertions(+), 6 deletions(-)
> 
> diff --git a/include/sound/compress_driver.h b/include/sound/compress_driver.h
> index 70cbc5095e72..8d23351f7ad7 100644
> --- a/include/sound/compress_driver.h
> +++ b/include/sound/compress_driver.h
> @@ -93,6 +93,9 @@ struct snd_compr_stream {
>    * @set_params: Sets the compressed stream parameters, mandatory
>    * This can be called in during stream creation only to set codec params
>    * and the stream properties
> + * @set_codec_params: Sets the compressed stream codec parameters, mandatory
> + * This can be called in during gapless next track codec change only to set
> + * codec params
>    * @get_params: retrieve the codec parameters, mandatory
>    * @set_metadata: Set the metadata values for a stream
>    * @get_metadata: retrieves the requested metadata values from stream
> @@ -112,6 +115,8 @@ struct snd_compr_ops {
>   	int (*free)(struct snd_compr_stream *stream);
>   	int (*set_params)(struct snd_compr_stream *stream,
>   			struct snd_compr_params *params);
> +	int (*set_codec_params)(struct snd_compr_stream *stream,
> +			struct snd_codec *params);
>   	int (*get_params)(struct snd_compr_stream *stream,
>   			struct snd_codec *params);
>   	int (*set_metadata)(struct snd_compr_stream *stream,
> diff --git a/include/sound/soc-component.h b/include/sound/soc-component.h
> index 5663891148e3..1e69c54ed0b9 100644
> --- a/include/sound/soc-component.h
> +++ b/include/sound/soc-component.h
> @@ -36,6 +36,9 @@ struct snd_compress_ops {
>   	int (*get_params)(struct snd_soc_component *component,
>   			  struct snd_compr_stream *stream,
>   			  struct snd_codec *params);
> +	int (*set_codec_params)(struct snd_soc_component *component,
> +			  struct snd_compr_stream *stream,
> +			  struct snd_codec *params);
>   	int (*set_metadata)(struct snd_soc_component *component,
>   			    struct snd_compr_stream *stream,
>   			    struct snd_compr_metadata *metadata);
> diff --git a/include/sound/soc-dai.h b/include/sound/soc-dai.h
> index 212257e84fac..526794ee555b 100644
> --- a/include/sound/soc-dai.h
> +++ b/include/sound/soc-dai.h
> @@ -192,6 +192,9 @@ int snd_soc_dai_compr_trigger(struct snd_soc_dai *dai,
>   int snd_soc_dai_compr_set_params(struct snd_soc_dai *dai,
>   				 struct snd_compr_stream *cstream,
>   				 struct snd_compr_params *params);
> +int snd_soc_dai_compr_set_codec_params(struct snd_soc_dai *dai,
> +				 struct snd_compr_stream *cstream,
> +				 struct snd_codec *codec);
>   int snd_soc_dai_compr_get_params(struct snd_soc_dai *dai,
>   				 struct snd_compr_stream *cstream,
>   				 struct snd_codec *params);
> @@ -292,6 +295,8 @@ struct snd_soc_cdai_ops {
>   			struct snd_soc_dai *);
>   	int (*set_params)(struct snd_compr_stream *,
>   			struct snd_compr_params *, struct snd_soc_dai *);
> +	int (*set_codec_params)(struct snd_compr_stream *,
> +			struct snd_codec *, struct snd_soc_dai *);
>   	int (*get_params)(struct snd_compr_stream *,
>   			struct snd_codec *, struct snd_soc_dai *);
>   	int (*set_metadata)(struct snd_compr_stream *,
> diff --git a/include/uapi/sound/compress_offload.h b/include/uapi/sound/compress_offload.h
> index 7184265c0b0d..c46286113a4b 100644
> --- a/include/uapi/sound/compress_offload.h
> +++ b/include/uapi/sound/compress_offload.h
> @@ -172,6 +172,7 @@ struct snd_compr_metadata {
>   						 struct snd_compr_metadata)
>   #define SNDRV_COMPRESS_GET_METADATA	_IOWR('C', 0x15,\
>   						 struct snd_compr_metadata)
> +#define SNDRV_COMPRESS_SET_CODEC_PARAMS	_IOW('C', 0x16, struct snd_codec)
>   #define SNDRV_COMPRESS_TSTAMP		_IOR('C', 0x20, struct snd_compr_tstamp)
>   #define SNDRV_COMPRESS_AVAIL		_IOR('C', 0x21, struct snd_compr_avail)
>   #define SNDRV_COMPRESS_PAUSE		_IO('C', 0x30)
> diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c
> index 0e53f6f31916..1c4b2cf450a0 100644
> --- a/sound/core/compress_offload.c
> +++ b/sound/core/compress_offload.c
> @@ -566,6 +566,18 @@ static int snd_compr_allocate_buffer(struct snd_compr_stream *stream,
>   	return 0;
>   }
>   
> +static int snd_compress_check_codec_params(struct snd_codec *codec)
> +{
> +	/* now codec parameters */
> +	if (codec->id == 0 || codec->id > SND_AUDIOCODEC_MAX)
> +		return -EINVAL;
> +
> +	if (codec->ch_in == 0 || codec->ch_out == 0)
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
>   static int snd_compress_check_input(struct snd_compr_params *params)
>   {
>   	/* first let's check the buffer parameter's */
> @@ -574,14 +586,41 @@ static int snd_compress_check_input(struct snd_compr_params *params)
>   	    params->buffer.fragments == 0)
>   		return -EINVAL;
>   
> -	/* now codec parameters */
> -	if (params->codec.id == 0 || params->codec.id > SND_AUDIOCODEC_MAX)
> -		return -EINVAL;
> +	return snd_compress_check_codec_params(&params->codec);
>   
> -	if (params->codec.ch_in == 0 || params->codec.ch_out == 0)
> -		return -EINVAL;
> +}
>   
> -	return 0;
> +static int snd_compr_set_codec_params(struct snd_compr_stream *stream,
> +				      unsigned long arg)
> +{
> +	struct snd_codec *params;
> +	int retval;
> +
> +	if (!stream->ops->set_codec_params)
> +		return -EPERM;
> +
> +	if (stream->runtime->state != SNDRV_PCM_STATE_RUNNING)
> +		return -EPERM;
> +
> +	/* codec params can be only set when next track has been signalled */
> +	if (stream->next_track == false)
> +		return -EPERM;
> +
> +	params = memdup_user((void __user *)arg, sizeof(*params));
> +	if (IS_ERR(params))
> +		return PTR_ERR(params);
> +
> +	retval = snd_compress_check_codec_params(params);
> +	if (retval)
> +		goto out;
> +
> +	retval = stream->ops->set_codec_params(stream, params);
> +	if (retval)
> +		goto out;
> +
> +out:
> +	kfree(params);
> +	return retval;
>   }
>   
>   static int
> @@ -964,6 +1003,9 @@ static long snd_compr_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
>   	case _IOC_NR(SNDRV_COMPRESS_SET_PARAMS):
>   		retval = snd_compr_set_params(stream, arg);
>   		break;
> +	case _IOC_NR(SNDRV_COMPRESS_SET_CODEC_PARAMS):
> +		retval = snd_compr_set_codec_params(stream, arg);
> +		break;
>   	case _IOC_NR(SNDRV_COMPRESS_GET_PARAMS):
>   		retval = snd_compr_get_params(stream, arg);
>   		break;
> diff --git a/sound/soc/soc-compress.c b/sound/soc/soc-compress.c
> index 4984b6a2c370..e549e0197aca 100644
> --- a/sound/soc/soc-compress.c
> +++ b/sound/soc/soc-compress.c
> @@ -518,6 +518,34 @@ static int soc_compr_set_params_fe(struct snd_compr_stream *cstream,
>   	return ret;
>   }
>   
> +static int soc_compr_set_codec_params(struct snd_compr_stream *cstream,
> +				      struct snd_codec *codec)
> +{
> +	struct snd_soc_pcm_runtime *rtd = cstream->private_data;
> +	struct snd_soc_component *component;
> +	struct snd_soc_dai *cpu_dai = asoc_rtd_to_cpu(rtd, 0);
> +	int i, ret;
> +
> +	mutex_lock_nested(&rtd->card->pcm_mutex, rtd->card->pcm_subclass);
> +
> +	ret = snd_soc_dai_compr_set_codec_params(cpu_dai, cstream, codec);
> +	if (ret < 0)
> +		goto err;
> +
> +	for_each_rtd_components(rtd, i, component) {
> +		if (!component->driver->compress_ops ||
> +		    !component->driver->compress_ops->set_codec_params)
> +			continue;
> +
> +		ret = component->driver->compress_ops->set_codec_params(component, cstream,
> +								     codec);
> +		break;
> +	}
> +err:
> +	mutex_unlock(&rtd->card->pcm_mutex);
> +	return ret;
> +}
> +
>   static int soc_compr_get_params(struct snd_compr_stream *cstream,
>   				struct snd_codec *params)
>   {
> @@ -728,6 +756,7 @@ static struct snd_compr_ops soc_compr_ops = {
>   	.open		= soc_compr_open,
>   	.free		= soc_compr_free,
>   	.set_params	= soc_compr_set_params,
> +	.set_codec_params = soc_compr_set_codec_params,
>   	.set_metadata   = soc_compr_set_metadata,
>   	.get_metadata	= soc_compr_get_metadata,
>   	.get_params	= soc_compr_get_params,
> @@ -744,6 +773,7 @@ static struct snd_compr_ops soc_compr_dyn_ops = {
>   	.free		= soc_compr_free_fe,
>   	.set_params	= soc_compr_set_params_fe,
>   	.get_params	= soc_compr_get_params,
> +	.set_codec_params = soc_compr_set_codec_params,
>   	.set_metadata   = soc_compr_set_metadata,
>   	.get_metadata	= soc_compr_get_metadata,
>   	.trigger	= soc_compr_trigger_fe,
> diff --git a/sound/soc/soc-dai.c b/sound/soc/soc-dai.c
> index b05e18b63a1c..06481d0278b8 100644
> --- a/sound/soc/soc-dai.c
> +++ b/sound/soc/soc-dai.c
> @@ -594,6 +594,20 @@ int snd_soc_dai_compr_get_params(struct snd_soc_dai *dai,
>   }
>   EXPORT_SYMBOL_GPL(snd_soc_dai_compr_get_params);
>   
> +int snd_soc_dai_compr_set_codec_params(struct snd_soc_dai *dai,
> +					struct snd_compr_stream *cstream,
> +					struct snd_codec *codec)
> +{	int ret = 0;
> +
> +	if (dai->driver->cops &&
> +	    dai->driver->cops->set_codec_params)
> +		ret = dai->driver->cops->set_codec_params(cstream, codec, dai);
> +
> +	return soc_dai_ret(dai, ret);
> +
> +}
> +EXPORT_SYMBOL_GPL(snd_soc_dai_compr_set_codec_params);
> +
>   int snd_soc_dai_compr_ack(struct snd_soc_dai *dai,
>   			  struct snd_compr_stream *cstream,
>   			  size_t bytes)
>