Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6: (36 commits)
  ALSA: hda - Add VREF powerdown sequence for another board
  ALSA: oss - volume control for CSWITCH and CROUTE
  ALSA: hda - add missing comma in ad1884_slave_vols
  sound: usb-audio: allow period sizes less than 1 ms
  sound: usb-audio: save data packet interval in audioformat structure
  sound: usb-audio: remove check_hw_params_convention()
  sound: usb-audio: show sample format width in proc file
  ASoC: fsl_dma: Pass the proper device for dma mapping routines
  ASoC: Fix null dereference in ak4535_remove()
  ALSA: hda - enable SPDIF output for Intel DX58SO board
  ALSA: snd-atmel-abdac: increase periods_min to 6 instead of 4
  ALSA: snd-atmel-abdac: replace bus_id with dev_name()
  ALSA: snd-atmel-ac97c: replace bus_id with dev_name()
  ALSA: snd-atmel-ac97c: cleanup registers when removing driver
  ALSA: snd-atmel-ac97c: do a proper reset of the external codec
  ALSA: snd-atmel-ac97c: enable interrupts to catch events for error reporting
  ALSA: snd-atmel-ac97c: set correct size for buffer hardware parameter
  ALSA: snd-atmel-ac97c: do not overwrite OCA and ICA when assigning channels
  ALSA: snd-atmel-ac97c: remove dead break statements after return in switch case
  ALSA: snd-atmel-ac97c: cleanup register definitions
  ...

1 files changed, 71 insertions, 0 deletions

diff --git a/Documentation/sound/alsa/soc/jack.txt b/Documentation/sound/alsa/soc/jack.txt
new file mode 100644
index 000000000000..fcf82a417293
--- /dev/null
+++ b/Documentation/sound/alsa/soc/jack.txt
@@ -0,0 +1,71 @@
+ASoC jack detection
+===================
+
+ALSA has a standard API for representing physical jacks to user space,
+the kernel side of which can be seen in include/sound/jack.h.  ASoC
+provides a version of this API adding two additional features:
+
+ - It allows more than one jack detection method to work together on one
+   user visible jack.  In embedded systems it is common for multiple
+   to be present on a single jack but handled by separate bits of
+   hardware.
+
+ - Integration with DAPM, allowing DAPM endpoints to be updated
+   automatically based on the detected jack status (eg, turning off the
+   headphone outputs if no headphones are present).
+
+This is done by splitting the jacks up into three things working
+together: the jack itself represented by a struct snd_soc_jack, sets of
+snd_soc_jack_pins representing DAPM endpoints to update and blocks of
+code providing jack reporting mechanisms.
+
+For example, a system may have a stereo headset jack with two reporting
+mechanisms, one for the headphone and one for the microphone.  Some
+systems won't be able to use their speaker output while a headphone is
+connected and so will want to make sure to update both speaker and
+headphone when the headphone jack status changes.
+
+The jack - struct snd_soc_jack
+==============================
+
+This represents a physical jack on the system and is what is visible to
+user space.  The jack itself is completely passive, it is set up by the
+machine driver and updated by jack detection methods.
+
+Jacks are created by the machine driver calling snd_soc_jack_new().
+
+snd_soc_jack_pin
+================
+
+These represent a DAPM pin to update depending on some of the status
+bits supported by the jack.  Each snd_soc_jack has zero or more of these
+which are updated automatically.  They are created by the machine driver
+and associated with the jack using snd_soc_jack_add_pins().  The status
+of the endpoint may configured to be the opposite of the jack status if
+required (eg, enabling a built in microphone if a microphone is not
+connected via a jack).
+
+Jack detection methods
+======================
+
+Actual jack detection is done by code which is able to monitor some
+input to the system and update a jack by calling snd_soc_jack_report(),
+specifying a subset of bits to update.  The jack detection code should
+be set up by the machine driver, taking configuration for the jack to
+update and the set of things to report when the jack is connected.
+
+Often this is done based on the status of a GPIO - a handler for this is
+provided by the snd_soc_jack_add_gpio() function.  Other methods are
+also available, for example integrated into CODECs.  One example of
+CODEC integrated jack detection can be see in the WM8350 driver.
+
+Each jack may have multiple reporting mechanisms, though it will need at
+least one to be useful.
+
+Machine drivers
+===============
+
+These are all hooked together by the machine driver depending on the
+system hardware.  The machine driver will set up the snd_soc_jack and
+the list of pins to update then set up one or more jack detection
+mechanisms to update that jack based on their current status.