ASoC Machine Driver

The ASoC machine (or board) driver is the code that glues together all thecomponent drivers (e.g. codecs, platforms and DAIs). It also describes therelationships between each component which include audio paths, GPIOs,interrupts, clocking, jacks and voltage regulators.

The machine driver can contain codec and platform specific code. It registersthe audio subsystem with the kernel as a platform device and is represented bythe following struct:-

/* SoC machine */struct snd_soc_card {      char *name;      ...      int (*probe)(struct platform_device *pdev);      int (*remove)(struct platform_device *pdev);      /* the pre and post PM functions are used to do any PM work before and       * after the codec and DAIs do any PM work. */      int (*suspend_pre)(struct platform_device *pdev, pm_message_t state);      int (*suspend_post)(struct platform_device *pdev, pm_message_t state);      int (*resume_pre)(struct platform_device *pdev);      int (*resume_post)(struct platform_device *pdev);      ...      /* CPU <--> Codec DAI links  */      struct snd_soc_dai_link *dai_link;      int num_links;      ...};

probe()/remove()

probe/remove are optional. Do any machine specific probe here.

suspend()/resume()

The machine driver has pre and post versions of suspend and resume to take careof any machine audio tasks that have to be done before or after the codec, DAIsand DMA is suspended and resumed. Optional.

Machine DAI Configuration

The machine DAI configuration glues all the codec and CPU DAIs together. It canalso be used to set up the DAI system clock and for any machine related DAIinitialisation e.g. the machine audio map can be connected to the codec audiomap, unconnected codec pins can be set as such.

structsnd_soc_dai_link is used to set up each DAI in your machine. e.g.

/* corgi digital audio interface glue - connects codec <--> CPU */static struct snd_soc_dai_link corgi_dai = {      .name = "WM8731",      .stream_name = "WM8731",      .cpu_dai_name = "pxa-is2-dai",      .codec_dai_name = "wm8731-hifi",      .platform_name = "pxa-pcm-audio",      .codec_name = "wm8713-codec.0-001a",      .init = corgi_wm8731_init,      .ops = &corgi_ops,};

In the above struct, dai’s are registered using names but you can passeither dai name or device tree node but not both. Also, names used herefor cpu/codec/platform dais should be globally unique.

Additionally below example macro can be used to register cpu, codec andplatform dai:

SND_SOC_DAILINK_DEFS(wm2200_cpu_dsp,      DAILINK_COMP_ARRAY(COMP_CPU("samsung-i2s.0")),      DAILINK_COMP_ARRAY(COMP_CODEC("spi0.0", "wm0010-sdi1")),      DAILINK_COMP_ARRAY(COMP_PLATFORM("samsung-i2s.0")));

structsnd_soc_card then sets up the machine with its DAIs. e.g.

/* corgi audio machine driver */static struct snd_soc_card snd_soc_corgi = {      .name = "Corgi",      .dai_link = &corgi_dai,      .num_links = 1,};

Following this,devm_snd_soc_register_card can be used to registerthe sound card. During the registration, the individual componentssuch as the codec, CPU, and platform are probed. If all these componentsare successfully probed, the sound card gets registered.

Machine Power Map

The machine driver can optionally extend the codec power map and to become anaudio power map of the audio subsystem. This allows for automatic power up/downof speaker/HP amplifiers, etc. Codec pins can be connected to the machines jacksockets in the machine init function.

Machine Controls

Machine specific audio mixer controls can be added in the DAI init function.

Clocking Controls

As previously noted, clock configuration is handled within the machine driver.For details on the clock APIs that the machine driver can utilize forsetup, please refer toAudio Clocking. However, thecallback needs to be registered by the CPU/Codec/Platform drivers to configurethe clocks that is needed for the corresponding device operation.