Properly let PCM leave suspended state when hardware doesn't support PCM resume

[Kai-Heng Feng]

[Impact]
Headset Mic plugged into Dell WD19TB dock stops working after suspend/resume.

[Fix]
According to alia-lib's document, to make PCM properly leave suspended state, we only use snd_pcm_resume() if hardware support PCM resume.
For hardware that doesn't support PCM resume, like snd-usb-audio on WD19TB dock, we should use snd_pcm_prepare(), snd_pcm_drop() or snd_pcm_drain() to make device leave suspended state. This patch defaults to use snd_pcm_drop() to achieve the goal.

[Test]
1. See if microphone on snd-usb-audio works in gnome-control-center/cheese.
2. Suspend/resume.
3. See if microphone still works in those apps.
I can the issue is fixed after each suspend/resume cycle.

[Regression Potential]
Low. This fix makes PCM suspend/resume more reliable. No functional change intended. I also don't find any regression during some smoke test.

[Ubuntu Foundations Team Bug Bot (crichton)]

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[Daniel van Vugt (vanvugt)]

I just noticed the above patch. Now added to git:

https://git.launchpad.net/~ubuntu-audio-dev/pulseaudio/log/?h=ubuntu-bionic

Please remember to put proposed changes in git so everyone is working with the same source.

[Daniel van Vugt (vanvugt)]

Also please provide links to upstream changes/bugs in the patch, and/or here.

[Kai-Heng Feng (kaihengfeng)]

Doesn't seem to be have an upstream bug.

Here's the upstream commit:
https://gitlab.freedesktop.org/pulseaudio/pulseaudio/commit/f7b3537bbf9a6916ee3fd72a82025519b4c346f5

[Sebastien Bacher (seb128)]

The fix is in the current pulseaudio version/Ubuntu serie

[Sebastien Bacher (seb128)]

@Kai-Heng, you unassigned yourself, does it mean it's not important anymore for bionic and the target should be dropped?

[Kai-Heng Feng (kaihengfeng)]

I think it's okay to drop it since Focal is imminent.