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Diffstat (limited to 'Documentation/sound/alsa/soc/codec.txt')
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diff --git a/Documentation/sound/alsa/soc/codec.txt b/Documentation/sound/alsa/soc/codec.txt new file mode 100644 index 00000000000..48983c75aad --- /dev/null +++ b/Documentation/sound/alsa/soc/codec.txt @@ -0,0 +1,197 @@ +ASoC Codec Driver +================= + +The codec driver is generic and hardware independent code that configures the +codec to provide audio capture and playback. It should contain no code that is +specific to the target platform or machine. All platform and machine specific +code should be added to the platform and machine drivers respectively. + +Each codec driver *must* provide the following features:- + + 1) Codec DAI and PCM configuration + 2) Codec control IO - using I2C, 3 Wire(SPI) or both API's + 3) Mixers and audio controls + 4) Codec audio operations + +Optionally, codec drivers can also provide:- + + 5) DAPM description. + 6) DAPM event handler. + 7) DAC Digital mute control. + +It's probably best to use this guide in conjuction with the existing codec +driver code in sound/soc/codecs/ + +ASoC Codec driver breakdown +=========================== + +1 - Codec DAI and PCM configuration +----------------------------------- +Each codec driver must have a struct snd_soc_codec_dai to define it's DAI and +PCM's capablities and operations. This struct is exported so that it can be +registered with the core by your machine driver. + +e.g. + +struct snd_soc_codec_dai wm8731_dai = { + .name = "WM8731", + /* playback capabilities */ + .playback = { + .stream_name = "Playback", + .channels_min = 1, + .channels_max = 2, + .rates = WM8731_RATES, + .formats = WM8731_FORMATS,}, + /* capture capabilities */ + .capture = { + .stream_name = "Capture", + .channels_min = 1, + .channels_max = 2, + .rates = WM8731_RATES, + .formats = WM8731_FORMATS,}, + /* pcm operations - see section 4 below */ + .ops = { + .prepare = wm8731_pcm_prepare, + .hw_params = wm8731_hw_params, + .shutdown = wm8731_shutdown, + }, + /* DAI operations - see DAI.txt */ + .dai_ops = { + .digital_mute = wm8731_mute, + .set_sysclk = wm8731_set_dai_sysclk, + .set_fmt = wm8731_set_dai_fmt, + } +}; +EXPORT_SYMBOL_GPL(wm8731_dai); + + +2 - Codec control IO +-------------------- +The codec can ususally be controlled via an I2C or SPI style interface (AC97 +combines control with data in the DAI). The codec drivers will have to provide +functions to read and write the codec registers along with supplying a register +cache:- + + /* IO control data and register cache */ + void *control_data; /* codec control (i2c/3wire) data */ + void *reg_cache; + +Codec read/write should do any data formatting and call the hardware read write +below to perform the IO. These functions are called by the core and alsa when +performing DAPM or changing the mixer:- + + unsigned int (*read)(struct snd_soc_codec *, unsigned int); + int (*write)(struct snd_soc_codec *, unsigned int, unsigned int); + +Codec hardware IO functions - usually points to either the I2C, SPI or AC97 +read/write:- + + hw_write_t hw_write; + hw_read_t hw_read; + + +3 - Mixers and audio controls +----------------------------- +All the codec mixers and audio controls can be defined using the convenience +macros defined in soc.h. + + #define SOC_SINGLE(xname, reg, shift, mask, invert) + +Defines a single control as follows:- + + xname = Control name e.g. "Playback Volume" + reg = codec register + shift = control bit(s) offset in register + mask = control bit size(s) e.g. mask of 7 = 3 bits + invert = the control is inverted + +Other macros include:- + + #define SOC_DOUBLE(xname, reg, shift_left, shift_right, mask, invert) + +A stereo control + + #define SOC_DOUBLE_R(xname, reg_left, reg_right, shift, mask, invert) + +A stereo control spanning 2 registers + + #define SOC_ENUM_SINGLE(xreg, xshift, xmask, xtexts) + +Defines an single enumerated control as follows:- + + xreg = register + xshift = control bit(s) offset in register + xmask = control bit(s) size + xtexts = pointer to array of strings that describe each setting + + #define SOC_ENUM_DOUBLE(xreg, xshift_l, xshift_r, xmask, xtexts) + +Defines a stereo enumerated control + + +4 - Codec Audio Operations +-------------------------- +The codec driver also supports the following alsa operations:- + +/* SoC audio ops */ +struct snd_soc_ops { + int (*startup)(struct snd_pcm_substream *); + void (*shutdown)(struct snd_pcm_substream *); + int (*hw_params)(struct snd_pcm_substream *, struct snd_pcm_hw_params *); + int (*hw_free)(struct snd_pcm_substream *); + int (*prepare)(struct snd_pcm_substream *); +}; + +Please refer to the alsa driver PCM documentation for details. +http://www.alsa-project.org/~iwai/writing-an-alsa-driver/c436.htm + + +5 - DAPM description. +--------------------- +The Dynamic Audio Power Management description describes the codec's power +components, their relationships and registers to the ASoC core. Please read +dapm.txt for details of building the description. + +Please also see the examples in other codec drivers. + + +6 - DAPM event handler +---------------------- +This function is a callback that handles codec domain PM calls and system +domain PM calls (e.g. suspend and resume). It's used to put the codec to sleep +when not in use. + +Power states:- + + SNDRV_CTL_POWER_D0: /* full On */ + /* vref/mid, clk and osc on, active */ + + SNDRV_CTL_POWER_D1: /* partial On */ + SNDRV_CTL_POWER_D2: /* partial On */ + + SNDRV_CTL_POWER_D3hot: /* Off, with power */ + /* everything off except vref/vmid, inactive */ + + SNDRV_CTL_POWER_D3cold: /* Everything Off, without power */ + + +7 - Codec DAC digital mute control. +------------------------------------ +Most codecs have a digital mute before the DAC's that can be used to minimise +any system noise. The mute stops any digital data from entering the DAC. + +A callback can be created that is called by the core for each codec DAI when the +mute is applied or freed. + +i.e. + +static int wm8974_mute(struct snd_soc_codec *codec, + struct snd_soc_codec_dai *dai, int mute) +{ + u16 mute_reg = wm8974_read_reg_cache(codec, WM8974_DAC) & 0xffbf; + if(mute) + wm8974_write(codec, WM8974_DAC, mute_reg | 0x40); + else + wm8974_write(codec, WM8974_DAC, mute_reg); + return 0; +} |