On 2015-11-02 08:30, Yang, Libin wrote:
4. power management
If we close the PCM when disconnecting monitor, the driver will
return
-ENODEV, and we assume user space will close the PCM at once .
... if we implement it. Actually this behavior (returning -ENODEV) is
not mandatory and needs investigation beforehand, whether this
breaks
any applications, especially PA.
Yes. I heard that PA has dummy PCM and when there is no HW to
play the audio, PA can smoothly move the PCM from HW to dummy
PCM. If it's true, stopping PCM will not break PA, I think.
Well, in most cases (not all) there will be an analog output available,
so we're more likely to move there than to a dummy PCM. The problem is
that PA does not currently figure out that a -ENODEV means that one
should switch from a digital to an analog profile. So, at least at this
point, don't expect a "smooth move".
I'm not sure if this is a good idea or not, but just brainstorming here:
If PA (or other application) tries to play back to a PCM, and that PCM
is currently unassigned. What would happen if we actually assigned a
converter node at that point, but no pin node connected to that
converter node? Would that give a backwards compatible behaviour? I e,
audio userspace could successfully play back audio through the converter
node, but then the audio goes nowhere because there is no pin node assigned?
(Or perhaps we PA developers should actually start supporting this
properly like we said that we should do, for like three years or
something...)
// David
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