Re: [PATCH v4] ALSA: compress_offload: introduce passthrough operation mode

[Jaroslav Kysela <perex@xxxxxxxx>]

On 24. 06. 24 16:47, Vinod Koul wrote:
> Hi Jaroslav,

Hi Vinod,

> On 24-06-24, 15:58, Jaroslav Kysela wrote:
> > There is a requirement to expose the audio hardware that accelerates various
> > tasks for user space such as sample rate converters, compressed
> > stream decoders, etc.
>
> Can you please tell me more about this requirement. The initial view of
> compressed API was data only and use alsa kcontrols to handle the DSP
> functions? I would like to understand why we need a new API.

There are very long threads for v4l audio support - last v15 thread:

https://lore.kernel.org/linux-media/1710834674-3285-1-git-send-email-shengjiu.wang@xxxxxxx/

So the goal is to create something more efficient for the offload work, when 
the data (decoded/converted) should be returned back to the user space.

> What about the user of this API, i would like to see that as well

Any audio streaming framework like gstreamer or ffmpeg who can accelerate 
stream conversions in hardware for capable devices.

> > +A new direction SND_COMPRESS_PASSTHROUGH is introduced to identify
> > +the passthrough API.
>
> Is passthrough really a new good new name, this suggests data being
> passed thru but that is not the case...

It's something like "PASS data THROUGH kernel/driver". So it makes sense. My 
alternate name may be ACCEL (like acceleration).

> Wouldn't a control device be better or something else?

Compress API handles already enumeration and capabilities, so they can be 
extended for this purpose. Only I/O is different. Basically, we can reuse half 
of API from the current compress-offload API. It's really close thing (and 
it's also offload work).

> > +/**
> > + * struct snd_compr_task_runtime: task runtime description
>
> Can we add the description here for these..

Yes, I'll do.

> > + *
> > + */
> > +struct snd_compr_task_runtime {

...

> >   /**
> >    * struct snd_compr_runtime: runtime stream description
> >    * @state: stream state
>
> here as well, am sure it gives a warning now for missing description

I'll do.

				Thanks,
					Jaroslav

--
Jaroslav Kysela <perex@xxxxxxxx>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.