Merge tag 'docs-4.10' of git://git.lwn.net/linux

Pull documentation update from Jonathan Corbet:
 "These are the documentation changes for 4.10.

  It's another busy cycle for the docs tree, as the sphinx conversion
  continues. Highlights include:

   - Further work on PDF output, which remains a bit of a pain but
     should be more solid now.

   - Five more DocBook template files converted to Sphinx. Only 27 to
     go... Lots of plain-text files have also been converted and
     integrated.

   - Images in binary formats have been replaced with more
     source-friendly versions.

   - Various bits of organizational work, including the renaming of
     various files discussed at the kernel summit.

   - New documentation for the device_link mechanism.

  ... and, of course, lots of typo fixes and small updates"

* tag 'docs-4.10' of git://git.lwn.net/linux: (193 commits)
  dma-buf: Extract dma-buf.rst
  Update Documentation/00-INDEX
  docs: 00-INDEX: document directories/files with no docs
  docs: 00-INDEX: remove non-existing entries
  docs: 00-INDEX: add missing entries for documentation files/dirs
  docs: 00-INDEX: consolidate process/ and admin-guide/ description
  scripts: add a script to check if Documentation/00-INDEX is sane
  Docs: change sh -> awk in REPORTING-BUGS
  Documentation/core-api/device_link: Add initial documentation
  core-api: remove an unexpected unident
  ppc/idle: Add documentation for powersave=off
  Doc: Correct typo, "Introdution" => "Introduction"
  Documentation/atomic_ops.txt: convert to ReST markup
  Documentation/local_ops.txt: convert to ReST markup
  Documentation/assoc_array.txt: convert to ReST markup
  docs-rst: parse-headers.pl: cleanup the documentation
  docs-rst: fix media cleandocs target
  docs-rst: media/Makefile: reorganize the rules
  docs-rst: media: build SVG from graphviz files
  docs-rst: replace bayer.png by a SVG image
  ...

1 files changed, 55 insertions, 0 deletions

diff --git a/Documentation/sound/soc/pops-clicks.rst b/Documentation/sound/soc/pops-clicks.rst
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+=====================
+Audio Pops and Clicks
+=====================
+
+Pops and clicks are unwanted audio artifacts caused by the powering up and down
+of components within the audio subsystem. This is noticeable on PCs when an
+audio module is either loaded or unloaded (at module load time the sound card is
+powered up and causes a popping noise on the speakers).
+
+Pops and clicks can be more frequent on portable systems with DAPM. This is
+because the components within the subsystem are being dynamically powered
+depending on the audio usage and this can subsequently cause a small pop or
+click every time a component power state is changed.
+
+
+Minimising Playback Pops and Clicks
+===================================
+
+Playback pops in portable audio subsystems cannot be completely eliminated
+currently, however future audio codec hardware will have better pop and click
+suppression.  Pops can be reduced within playback by powering the audio
+components in a specific order. This order is different for startup and
+shutdown and follows some basic rules:-
+::
+
+   Startup Order :- DAC --> Mixers --> Output PGA --> Digital Unmute
+  
+   Shutdown Order :- Digital Mute --> Output PGA --> Mixers --> DAC
+
+This assumes that the codec PCM output path from the DAC is via a mixer and then
+a PGA (programmable gain amplifier) before being output to the speakers.
+
+
+Minimising Capture Pops and Clicks
+==================================
+
+Capture artifacts are somewhat easier to get rid as we can delay activating the
+ADC until all the pops have occurred. This follows similar power rules to
+playback in that components are powered in a sequence depending upon stream
+startup or shutdown.
+::
+
+   Startup Order - Input PGA --> Mixers --> ADC
+  
+   Shutdown Order - ADC --> Mixers --> Input PGA
+
+
+Zipper Noise
+============
+An unwanted zipper noise can occur within the audio playback or capture stream
+when a volume control is changed near its maximum gain value. The zipper noise
+is heard when the gain increase or decrease changes the mean audio signal
+amplitude too quickly. It can be minimised by enabling the zero cross setting
+for each volume control. The ZC forces the gain change to occur when the signal
+crosses the zero amplitude line.