Based on kernel version 4.9. Page generated on 2016-12-21 14:37 EST.
1 ASoC Codec Class Driver 2 ======================= 3 4 The codec class driver is generic and hardware independent code that configures 5 the codec, FM, MODEM, BT or external DSP to provide audio capture and playback. 6 It should contain no code that is specific to the target platform or machine. 7 All platform and machine specific code should be added to the platform and 8 machine drivers respectively. 9 10 Each codec class driver *must* provide the following features:- 11 12 1) Codec DAI and PCM configuration 13 2) Codec control IO - using RegMap API 14 3) Mixers and audio controls 15 4) Codec audio operations 16 5) DAPM description. 17 6) DAPM event handler. 18 19 Optionally, codec drivers can also provide:- 20 21 7) DAC Digital mute control. 22 23 Its probably best to use this guide in conjunction with the existing codec 24 driver code in sound/soc/codecs/ 25 26 ASoC Codec driver breakdown 27 =========================== 28 29 1 - Codec DAI and PCM configuration 30 ----------------------------------- 31 Each codec driver must have a struct snd_soc_dai_driver to define its DAI and 32 PCM capabilities and operations. This struct is exported so that it can be 33 registered with the core by your machine driver. 34 35 e.g. 36 37 static struct snd_soc_dai_ops wm8731_dai_ops = { 38 .prepare = wm8731_pcm_prepare, 39 .hw_params = wm8731_hw_params, 40 .shutdown = wm8731_shutdown, 41 .digital_mute = wm8731_mute, 42 .set_sysclk = wm8731_set_dai_sysclk, 43 .set_fmt = wm8731_set_dai_fmt, 44 }; 45 46 struct snd_soc_dai_driver wm8731_dai = { 47 .name = "wm8731-hifi", 48 .playback = { 49 .stream_name = "Playback", 50 .channels_min = 1, 51 .channels_max = 2, 52 .rates = WM8731_RATES, 53 .formats = WM8731_FORMATS,}, 54 .capture = { 55 .stream_name = "Capture", 56 .channels_min = 1, 57 .channels_max = 2, 58 .rates = WM8731_RATES, 59 .formats = WM8731_FORMATS,}, 60 .ops = &wm8731_dai_ops, 61 .symmetric_rates = 1, 62 }; 63 64 65 2 - Codec control IO 66 -------------------- 67 The codec can usually be controlled via an I2C or SPI style interface 68 (AC97 combines control with data in the DAI). The codec driver should use the 69 Regmap API for all codec IO. Please see include/linux/regmap.h and existing 70 codec drivers for example regmap usage. 71 72 73 3 - Mixers and audio controls 74 ----------------------------- 75 All the codec mixers and audio controls can be defined using the convenience 76 macros defined in soc.h. 77 78 #define SOC_SINGLE(xname, reg, shift, mask, invert) 79 80 Defines a single control as follows:- 81 82 xname = Control name e.g. "Playback Volume" 83 reg = codec register 84 shift = control bit(s) offset in register 85 mask = control bit size(s) e.g. mask of 7 = 3 bits 86 invert = the control is inverted 87 88 Other macros include:- 89 90 #define SOC_DOUBLE(xname, reg, shift_left, shift_right, mask, invert) 91 92 A stereo control 93 94 #define SOC_DOUBLE_R(xname, reg_left, reg_right, shift, mask, invert) 95 96 A stereo control spanning 2 registers 97 98 #define SOC_ENUM_SINGLE(xreg, xshift, xmask, xtexts) 99 100 Defines an single enumerated control as follows:- 101 102 xreg = register 103 xshift = control bit(s) offset in register 104 xmask = control bit(s) size 105 xtexts = pointer to array of strings that describe each setting 106 107 #define SOC_ENUM_DOUBLE(xreg, xshift_l, xshift_r, xmask, xtexts) 108 109 Defines a stereo enumerated control 110 111 112 4 - Codec Audio Operations 113 -------------------------- 114 The codec driver also supports the following ALSA PCM operations:- 115 116 /* SoC audio ops */ 117 struct snd_soc_ops { 118 int (*startup)(struct snd_pcm_substream *); 119 void (*shutdown)(struct snd_pcm_substream *); 120 int (*hw_params)(struct snd_pcm_substream *, struct snd_pcm_hw_params *); 121 int (*hw_free)(struct snd_pcm_substream *); 122 int (*prepare)(struct snd_pcm_substream *); 123 }; 124 125 Please refer to the ALSA driver PCM documentation for details. 126 http://www.alsa-project.org/~iwai/writing-an-alsa-driver/ 127 128 129 5 - DAPM description. 130 --------------------- 131 The Dynamic Audio Power Management description describes the codec power 132 components and their relationships and registers to the ASoC core. 133 Please read dapm.txt for details of building the description. 134 135 Please also see the examples in other codec drivers. 136 137 138 6 - DAPM event handler 139 ---------------------- 140 This function is a callback that handles codec domain PM calls and system 141 domain PM calls (e.g. suspend and resume). It is used to put the codec 142 to sleep when not in use. 143 144 Power states:- 145 146 SNDRV_CTL_POWER_D0: /* full On */ 147 /* vref/mid, clk and osc on, active */ 148 149 SNDRV_CTL_POWER_D1: /* partial On */ 150 SNDRV_CTL_POWER_D2: /* partial On */ 151 152 SNDRV_CTL_POWER_D3hot: /* Off, with power */ 153 /* everything off except vref/vmid, inactive */ 154 155 SNDRV_CTL_POWER_D3cold: /* Everything Off, without power */ 156 157 158 7 - Codec DAC digital mute control 159 ---------------------------------- 160 Most codecs have a digital mute before the DACs that can be used to 161 minimise any system noise. The mute stops any digital data from 162 entering the DAC. 163 164 A callback can be created that is called by the core for each codec DAI 165 when the mute is applied or freed. 166 167 i.e. 168 169 static int wm8974_mute(struct snd_soc_dai *dai, int mute) 170 { 171 struct snd_soc_codec *codec = dai->codec; 172 u16 mute_reg = snd_soc_read(codec, WM8974_DAC) & 0xffbf; 173 174 if (mute) 175 snd_soc_write(codec, WM8974_DAC, mute_reg | 0x40); 176 else 177 snd_soc_write(codec, WM8974_DAC, mute_reg); 178 return 0; 179 }