[alsa-devel] [PATCH v3 01/10] ALSA: hda/hdmi - implement mst_no_extra_pcms flag

[Kai Vehmanen]

Hey,

On Tue, 10 Sep 2019, Pierre-Louis Bossart wrote:

> 
> 
> On 9/10/19 1:29 PM, Kai Vehmanen wrote:
> > When mst_no_extra_pcms flag is set, the codec should not
> > use backup PCMs to handle DP-MST scenarios. Instead a simple
> > 1:1 mapping is assumed between PCMs and converters.
> 
> mst_no_extra_pcms is not set, which makes it hard to review and get the
> picture of what this does.

this flag is used in patch 3 of the series. I didn't want to combine the 
patches 1&3 as patch 3 is modifying sound/soc/codecs/hdac_hda.c.

Let me try to improve the commit message a bit to explain why this
is needed. In short, if patch_hdmi.c creates virtual PCMs for routing 
purposes (current behaviour with snd_hda_intel in non-DSP mode), it will 
be impossible to match them to PCMs in ASoC topology. Thus to enable users
like SOF (could be others), patch_hdmi.c needs to expose a mode where 
physical converters are mapped to a fixed set of PCMs (-> this is 
the mst_no_extra_pcms mode).

Br, Kai