[alsa-devel] ALSA concurrent use case for 5.1 LPCM on HDMI.

[Liam Girdwood]

On Wed, 2012-07-25 at 01:37 -0700, gsantosh at codeaurora.org wrote:
> Hi All,
> 
> I have following use case I am facing an issue with the ALSA framework,
> 
> Consider a use case
> 
> 1)	System tone or any stream running on Front End 0 with stereo channel
> configuration On Back End 0(HDMI)
> 2)	Start a local file playback for 5.1 LPCM on Front End 1 with 5.1
> channel configuration On Back End 0(HDMI)
> 
> Here FE0 and FE1 is routed to same BE0.
> 
> When step 2 is done I see following behavior of ALSA which is not correct.
> Framework will check that the BE0 is running with FE0 routed and running,
> Framework will not trigger the fixup and hw_params callback to re
> configure the session for FE1 with 5.1 channel.
> 
> With this effect we are playing the FE1 session with stereo instead of 5.1
> channel configuration, how to rectify this issue?
> 

Hmm, the fixup code will currently only run when the BE0 is initially
configured via hw_params(). The problem here is that if we fixup and
reconfigure BE0 (via hw_params()) after it is running then this will
likely cause undesired audio artifacts on BE0 (since in this case it's
already playing stereo and we want to change to 6 channel).

We have a similar situation with OMAP where we support many channels (2
- 6) on one McBSP BE DAI. We always configure the BE McBSP in 6 channel
mode and that allows us to open any FE with 2...6 channels (without a
fixup and restart of the McBSP port). 

Regards

Liam

> Regards,
> Santosh M G.
> 
> 
> 
>