Messages in this thread | | | Subject | Re: [PATCH 10/11] ASoC: qdsp6-dai: add gapless support | From | Srinivas Kandagatla <> | Date | Wed, 8 Jul 2020 16:23:19 +0100 |
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On 08/07/2020 14:32, Pierre-Louis Bossart wrote: > >>>> Add support to gapless playback by implementing metadata, >>>> next_track, drain and partial drain support. >>>> >>>> Gapless on Q6ASM is implemented by opening 2 streams in a single asm >>>> stream >>> >>> What does 'in a single asm stream' means? >> >> >> So in QDSP6 ASM (Audio Stream Manager) terminology we have something >> called "asm session" for each ASoC FE DAI, Each asm session can be >> connected with multiple streams (upto 8 I think). However there will >> be only one active stream at anytime. Also there only single data >> buffer associated with each asm session. >> >> For Gapless usecase, we can keep two streams open for one asm-session, >> allowing us to fill in data on second stream while first stream is >> playing. > > Ah, that's interesting, thanks for the details. So you have one DMA > transfer and the data from the previous and next track are provided in > consecutive bytes in a ring buffer, but at the DSP level you have a > switch that will feed data for the previous and next tracks into > different decoders, yes?
Yes, that's true, we can drain and stop first stream and start next stream which will do the switch!
> > If that is the case, indeed the extension you suggested earlier to > change the profile is valid. You could even change the format I guess. >
Exactly, we did test this patchset along with the extension suggested!
> To avoid confusion I believe the capabilities would need to be extended > so that applications know that gapless playback is supported across > unrelated profiles/formats. The point is that you don't want a > traditional implementation to use a capability that isn't supported in > hardware or will lead to audio issues. > >>>> and toggling them on next track. >>> >>> It really seems to me that you have two streams at the lowest level, >>> along with the knowledge of how many samples to remove/insert and >>> hence could do a much better job - including gapless support between >>> unrelated profiles and cross-fading - without the partial drain and >>> next_track mechanism that was defined assuming a single stream/profile. >> At the end of the day its a single session with one data buffer but >> with multiple streams. >> >> Achieving cross fade should be easy with this design. > > looks like it indeed. > >> We need those hooks for partial drain and next track to allow us to >> switch between streams and pass silence information to respective >> stream ids. > > right, but the key point is 'switch between streams'. That means a more > complex/capable implementation that should be advertised as such to > applications. This is not the default behavior assumed initially: to > allow for minimal implementations in memory-constrained devices, we > assumed gapless was supported with a single decoder. > > Maybe the right way to do this is extend the snd_compr_caps structure: > > /** > * struct snd_compr_caps - caps descriptor > * @codecs: pointer to array of codecs > * @direction: direction supported. Of type snd_compr_direction > * @min_fragment_size: minimum fragment supported by DSP > * @max_fragment_size: maximum fragment supported by DSP > * @min_fragments: min fragments supported by DSP > * @max_fragments: max fragments supported by DSP > * @num_codecs: number of codecs supported > * @reserved: reserved field > */ > struct snd_compr_caps { > __u32 num_codecs; > __u32 direction; > __u32 min_fragment_size; > __u32 max_fragment_size; > __u32 min_fragments; > __u32 max_fragments; > __u32 codecs[MAX_NUM_CODECS]; > __u32 reserved[11]; > } __attribute__((packed, aligned(4))); > > > and use a reserved field to provide info on capabilities, and filter the > set_codec_params() addition based this capability - i.e. return -ENOTSUP > in 'traditional' implementations based on a single 'stream'/decoder > instance. Sounds good! I will give it a go and see how it ends up!
--srini
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