[Bug 1929817] Re: [SRU] pulseaudio: let a single alsa mixer support up to 8 channels (focal only)

[Hui Wang]

** Summary changed:

- [SRU] pulseaudio: let a signle alsa mixer support up to 8 channels
+ [SRU] pulseaudio: let a single alsa mixer support up to 8 channels (focal only)

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Title:
  [SRU] pulseaudio: let a single alsa mixer support up to 8 channels
  (focal only)

Status in pulseaudio package in Ubuntu:
  In Progress
Status in pulseaudio source package in Focal:
  In Progress

Bug description:
  [Impact]
  Many Lenovo laptops have up to 4 microphones (microphone array), before the linux kernel 5.11, the alsa mixer for digital microphone is 2 channels, and the PA in the focal also supports up to 2 chanels for a single alsa mixer, so the PA in the focal works well with linux kernel 5.10 and lower on those Lenovo laptops. But we are going to install hirsute kernel (5.11) to the focal, the PA in the focal can't handle 4 channels of the digital mic, it will use pure software volume for digital mic, user can't adjust hardware volume of the digital mic anymore.

  
  [Fix]
  Backport 2 patches from PA-14.2, the PA in the hirsute (21.04) already have these 2 patches, so this SRU is for focal only. After applying these 2 patches, the PA could handle up to 8 channels for a single alsa mixer. 

  [Test]
  Install patched PA on Lenovo laptops with 4 digital microphone, I could change the hardware input volume of digital mic through pulseaudio. I also installed patched PA to some old lenovo and Dell machines, all output and input devices worked as well as before, there is no regression observed.

  [Where problems could occur]
  This could introduce a regression on the output/input volume control, for example, the output or input volume only supports software volume in the PA, users can't adjust the hardware volume through pulseaudio anymore. But this regression possibility is very low, first the hirsute already has these 2 patches, second I already tested these 2 patches on different machines, all worked as well as before.

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