> On 11/12/14, 9:02 PM, gsantosh@xxxxxxxxxxxxxx wrote: >> Hi All, >> >> The Question is for the compressed offload session. >> >> For a generic codec driver during the startup function it will set some >> of >> the hw_constraints rule similarly like this. >> >> snd_pcm_hw_constraint_list(substream->runtime, 0, >> SNDRV_PCM_HW_PARAM_RATE, >> &constraints_12_24); >> >> pcm_lib.c will try to add the rule to the runtime structure by accessing >> the pointers which will be initialized during opening of the session, >> as The Constraints added by the codec driver will be updated in the >> >> struct snd_pcm_hw_constraints of runtime structure which will be part of >> substream handle. >> >> But for the compressed offload I do not see the initialization done for >> HW >> constraints, as done in pcm session >> >> 2092int snd_pcm_open_substream(struct snd_pcm *pcm, int stream, >> 2093 struct file *file, >> 2094 struct snd_pcm_substream **rsubstream) >> >> most of the existing drivers which has the hw_constraint_list code will >> not be applicable for compress offload session, how to solve this? > > You can't directly link physical output/input with the decoder/encoder > in general. > For decoders, the sample-rate may not always be known ahead of time, > e.g. with AAC-SBR implicit signaling. There is no way to add constraints > on open, there is an assumption that a sample-rate converter is part of > the chain to take care of the difference between the output of the > offloaded decoder and the back-end actual sampling frequency (same with > number of channels and bit-width btw). > Likewise if you encode the frequency may not be the same as what the > backend provides and some SRC might be needed. > -Pierre > I Agree we cannot have a direct link between physical output / input with decoder / encoder, during compressed playback. My concern here is, if we have a legacy codec driver which is used for the PCM out, and in the start up of this codec driver it is adding hw_constraints list, now the same codec driver is used for the compressed session FE or PCM session FE, If the routing is such that compressed FE -> codec the hw_constraints added by this driver is not valid here, and legacy drivers needs to be changed, Now the question comes how to change this drivers? I can think of following things if the routing is done for Compressed FE -> codec 1) in Codec driver avoid adding hw_constraint during startup if compressed session is routed, this recommend for codec driver to know that compress session is routed to codec which I feel not the correct way to handle this I was checking how to handle this situation in much better way. Regards Santosh > _______________________________________________ > Alsa-devel mailing list > Alsa-devel@xxxxxxxxxxxxxxxx > http://mailman.alsa-project.org/mailman/listinfo/alsa-devel > -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
