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1ASoC jack detection 2=================== 3 4ALSA has a standard API for representing physical jacks to user space, 5the kernel side of which can be seen in include/sound/jack.h. ASoC 6provides a version of this API adding two additional features: 7 8 - It allows more than one jack detection method to work together on one 9 user visible jack. In embedded systems it is common for multiple 10 to be present on a single jack but handled by separate bits of 11 hardware. 12 13 - Integration with DAPM, allowing DAPM endpoints to be updated 14 automatically based on the detected jack status (eg, turning off the 15 headphone outputs if no headphones are present). 16 17This is done by splitting the jacks up into three things working 18together: the jack itself represented by a struct snd_soc_jack, sets of 19snd_soc_jack_pins representing DAPM endpoints to update and blocks of 20code providing jack reporting mechanisms. 21 22For example, a system may have a stereo headset jack with two reporting 23mechanisms, one for the headphone and one for the microphone. Some 24systems won't be able to use their speaker output while a headphone is 25connected and so will want to make sure to update both speaker and 26headphone when the headphone jack status changes. 27 28The jack - struct snd_soc_jack 29============================== 30 31This represents a physical jack on the system and is what is visible to 32user space. The jack itself is completely passive, it is set up by the 33machine driver and updated by jack detection methods. 34 35Jacks are created by the machine driver calling snd_soc_jack_new(). 36 37snd_soc_jack_pin 38================ 39 40These represent a DAPM pin to update depending on some of the status 41bits supported by the jack. Each snd_soc_jack has zero or more of these 42which are updated automatically. They are created by the machine driver 43and associated with the jack using snd_soc_jack_add_pins(). The status 44of the endpoint may configured to be the opposite of the jack status if 45required (eg, enabling a built in microphone if a microphone is not 46connected via a jack). 47 48Jack detection methods 49====================== 50 51Actual jack detection is done by code which is able to monitor some 52input to the system and update a jack by calling snd_soc_jack_report(), 53specifying a subset of bits to update. The jack detection code should 54be set up by the machine driver, taking configuration for the jack to 55update and the set of things to report when the jack is connected. 56 57Often this is done based on the status of a GPIO - a handler for this is 58provided by the snd_soc_jack_add_gpio() function. Other methods are 59also available, for example integrated into CODECs. One example of 60CODEC integrated jack detection can be see in the WM8350 driver. 61 62Each jack may have multiple reporting mechanisms, though it will need at 63least one to be useful. 64 65Machine drivers 66=============== 67 68These are all hooked together by the machine driver depending on the 69system hardware. The machine driver will set up the snd_soc_jack and 70the list of pins to update then set up one or more jack detection 71mechanisms to update that jack based on their current status.