Based on kernel version 4.9. Page generated on 2016-12-21 14:37 EST.
1 ASoC jack detection 2 =================== 3 4 ALSA has a standard API for representing physical jacks to user space, 5 the kernel side of which can be seen in include/sound/jack.h. ASoC 6 provides 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 17 This is done by splitting the jacks up into three things working 18 together: the jack itself represented by a struct snd_soc_jack, sets of 19 snd_soc_jack_pins representing DAPM endpoints to update and blocks of 20 code providing jack reporting mechanisms. 21 22 For example, a system may have a stereo headset jack with two reporting 23 mechanisms, one for the headphone and one for the microphone. Some 24 systems won't be able to use their speaker output while a headphone is 25 connected and so will want to make sure to update both speaker and 26 headphone when the headphone jack status changes. 27 28 The jack - struct snd_soc_jack 29 ============================== 30 31 This represents a physical jack on the system and is what is visible to 32 user space. The jack itself is completely passive, it is set up by the 33 machine driver and updated by jack detection methods. 34 35 Jacks are created by the machine driver calling snd_soc_jack_new(). 36 37 snd_soc_jack_pin 38 ================ 39 40 These represent a DAPM pin to update depending on some of the status 41 bits supported by the jack. Each snd_soc_jack has zero or more of these 42 which are updated automatically. They are created by the machine driver 43 and associated with the jack using snd_soc_jack_add_pins(). The status 44 of the endpoint may configured to be the opposite of the jack status if 45 required (eg, enabling a built in microphone if a microphone is not 46 connected via a jack). 47 48 Jack detection methods 49 ====================== 50 51 Actual jack detection is done by code which is able to monitor some 52 input to the system and update a jack by calling snd_soc_jack_report(), 53 specifying a subset of bits to update. The jack detection code should 54 be set up by the machine driver, taking configuration for the jack to 55 update and the set of things to report when the jack is connected. 56 57 Often this is done based on the status of a GPIO - a handler for this is 58 provided by the snd_soc_jack_add_gpio() function. Other methods are 59 also available, for example integrated into CODECs. One example of 60 CODEC integrated jack detection can be see in the WM8350 driver. 61 62 Each jack may have multiple reporting mechanisms, though it will need at 63 least one to be useful. 64 65 Machine drivers 66 =============== 67 68 These are all hooked together by the machine driver depending on the 69 system hardware. The machine driver will set up the snd_soc_jack and 70 the list of pins to update then set up one or more jack detection 71 mechanisms to update that jack based on their current status.