[alsa-devel] UCM extensions

[Cezary Rojewski]

On 2019-11-05 20:36, Jaroslav Kysela wrote:
> Hi all,
> 
>      I make some internal ucm code cleanups in alsa-lib and added three 
> major extensions to allow more complex configurations which we require 
> for the SOF kernel driver.
> 
>      The first thing is the added substitution for the value strings:
> 
> https://github.com/alsa-project/alsa-lib/commit/f1e637b285e8e04e6761248a070f58f3a8fde6fc 
> 
> 
>      The second thing is the If block:
> 
> https://github.com/alsa-project/alsa-lib/commit/985715ce8148dc7ef62c8e3d8ce5a0c2ac51f8df 
> 
> 
>      The third thing is the card / hardware like specifier passed as the 
> ucm name to snd_use_case_mgr_open() to support multiple card instances:
> 
> https://github.com/alsa-project/alsa-lib/commit/60164fc5886cdc6ca55eeed0c2e3f751a7d2b2c0 
> 
> 
>      All those patches (with other cleanups) are in the ucm2 branch on 
> github for comments:
> 
> https://github.com/alsa-project/alsa-lib/commits/ucm2
> 
>      The proposed SOF UCM config diff is here:
> 
> https://github.com/alsa-project/alsa-ucm-conf/commit/723b6da881721488229154e923ed36413955a051 
> 
> https://github.com/alsa-project/alsa-ucm-conf/commits/ucm2
> 
>      I added everything to keep the interface backward compatible, so 
> the current applications should not observe any different behavior. The 
> applications like pulseaudio should use the 'hw:CARD_INDEX' specifier 
> for the open call in the future and snd_use_case_parse_ctl_elem_id() 
> helper for the element control names.
> 
>      If you have another ideas to address those issues, please, let me 
> know.
> 
>      BTW, Mark: The SOF UCM configs relies on the driver name changes, 
> so it might be worth to send "ASoC: intel - fix the card names" patch to 
> 5.4 to make things stable more quickly:
> 
>      https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git/commit/?h=for-5.5&id=d745cc1ab65945b2d17ec9c5652f38299c054649
> 
>                  Thanks,
>                      Jaroslav
> 


Thanks for your work, Jaroslav.

However, I have some concerns here. First, could you elaborate on "we 
require for the SOF kernel driver"?

The substitutions and multi-instance support is probably warmly welcomed 
by many, but "If" blocks are what worries me. Especially the nested 
"Ifs". As Takashi pointed already out, UCM - which is currently is 
viewed as a simple configuration syntax - is becoming a language on its 
own. If we are to keep extending UCM on and on, we might as well switch 
to JSON/ XML/ YAML entirely instead of developing our own thingy.

"If" block could just be what's needed to open new pandora box, allowing 
for very complex and no longer easy-to-read config files. In general, if 
one is to enlist an "If", why not define two UCMs instead?

Moreover, I see you mentioning the card-name dependency. This sounds 
rather invasive. Separation of different config-versions would be required.

Czarek