On Mon, Sep 26, 2022 at 09:52:34AM +0200, Pierre-Louis Bossart wrote:
> On 9/26/22 03:34, Jason Zhu wrote:
> > 在 2022/9/23 20:55, Mark Brown 写道:

> >>> The data can not be lost in this process. So we attach VAD & PDM
> >>> in the same card, then close the card and wake up VAD & PDM again
> >>> when the system is goto sleep. Like these code:

> >> This sounds like a very normal thing with a standard audio stream -
> >> other devices have similar VAD stuff without needing to open code access
> >> to the PCM operations?

> > At present, only VAD is handled in this way by Rockchip.

The point here is that other non-Rockchip devices do similar sounding
things?

> >> Generally things just continue to stream the voice data through the same
> >> VAD stream IIRC - switching just adds complexity here, you don't have to
> >> deal with joining the VAD and regular streams up for one thing.

> > Yes, this looks complicated. But our chip's sram which is assigned to VAD
> > 
> > maybe used by other devices when the system is alive.  So we have to copy
> > 
> > sound data in sram firstly, then use the DDR(SDRAM) to record sound data.

> There are other devices that requires a copy of the history buffer from
> one PCM device and a software stitching with the real-time data coming
> from another PCM device. It's not ideal but not uncommon either, even
> for upcoming SDCA devices, combining data from 2 PCM devices will be an
> allowed option (with additional control information to help with the
> stitching).

If this is something that's not uncommon that sounds like an even
stronger reason for not just randomly exporting the symbols and open
coding things in individual drivers outside of framework control.  What
are these other use cases, or is it other instances of the same thing?

TBH this sounds like at least partly a userspace problem rather than a
kernel one, as with other things that tie multiple audio streams
together.