[alsa-devel] UCM extensions

[Jaroslav Kysela]

Dne 07. 11. 19 v 7:48 Takashi Iwai napsal(a):
> On Tue, 05 Nov 2019 20:36:28 +0100,
> 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.
> 
> The only concern with these extensions so far is the compatibility.
> Imagine that people run the new profile on the old parser, it'd break
> easily.
> 
> I think other scripts often installing on the versioned directory if
> incompatibilities are seen.  Can we do that for UCM as well?
> 
> Or course, once after UCM parser is changed to be future-ready and
> allow some syntax for possible future extensions, we can keep that
> version directory in future, too.

While we are going to separate UCM files from alsa-lib to alsa-ucm-conf we can 
define the new syntax change until the first version is released (I can put a 
notice to README).

Speaking for Fedora, we have dependancy 'alsa-lib package version' must be 
equal to 'alsa-ucm package version'. If users will do any changes on their 
own, they should know what they are doing.

Anyway, we should learn from this and I would propose to add add something 
like 'Syntax 2' to the main configuration file now. The new functions should 
be activated only according the version.

Unfortunately, the current parser will just show an error message like:

ALSA lib parser.c:1337:(parse_master_file) uknown master file field Syntax
ALSA lib parser.c:1337:(parse_master_file) uknown master file field If

But at least, users should be notified that there is a configuration mismatch.

Another possibility is to change the suffix for the master configuration file 
to accept the "Syntax" check for the another future update. But honestly, I 
don't like ".conf2" and ".v2.conf" looks not so nice, too.

					Jaroslav

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