[alsa-devel] [PATCH] ASoC: change 'HDMI/DP, pcm=' to 'HDMI/DP, pcm=' Jack control names

[Kai Vehmanen]

Hi Jaroslav and all,

On Fri, 25 Oct 2019, Jaroslav Kysela wrote:

> the single user. Another problem is that we are not able to review all those
> mistakes at the merge time. It is not a complain but a true fact.

but the strings are in kernel patches, so even if all UCM files don't 
go through the list, we can always review when the strings are added 
in kernel, right?

> I would be really curious what will happen when we change those strings ;-)

I can share some experiences that happen on Linux distros with Pulseaudio:

- if mixer control name is changed/missing that us used in 
  a UCM enable sequence, the enable sequence will fail and PA will
  not choose that device
	-> e.g. when wrong HDMI control names are in the UCM file, HDMI 
	output stops working
- if mixer control for a Jack is changed, PA will not listen
  for ALSA kctl events
	-> HDMI connection is silently missed and HDMI is not listed
	as a possible output

.. i.e. in both cases HDMI is essentially broken if you update to 
a kernel that updates the strings but don't update user-space in sync.

I wonder if one option would be to expose "legacy string" aliases,
allowing to make changes but keep existing user-space happy. With my HDMI 
codec change, the controls are simply different, so this was not an 
option and I had to opt for keeping the whole driver around.

Br, Kai