Based on kernel version 4.3. Page generated on 2015-11-02 12:51 EST.
1 Notes on Universal Interface for Intel High Definition Audio Codec 2 ------------------------------------------------------------------ 3 4 Takashi Iwai <tiwai@suse.de> 5 6 7 [Still a draft version] 8 9 10 General 11 ======= 12 13 The snd-hda-codec module supports the generic access function for the 14 High Definition (HD) audio codecs. It's designed to be independent 15 from the controller code like ac97 codec module. The real accessors 16 from/to the controller must be implemented in the lowlevel driver. 17 18 The structure of this module is similar with ac97_codec module. 19 Each codec chip belongs to a bus class which communicates with the 20 controller. 21 22 23 Initialization of Bus Instance 24 ============================== 25 26 The card driver has to create struct hda_bus at first. The template 27 struct should be filled and passed to the constructor: 28 29 struct hda_bus_template { 30 void *private_data; 31 struct pci_dev *pci; 32 const char *modelname; 33 struct hda_bus_ops ops; 34 }; 35 36 The card driver can set and use the private_data field to retrieve its 37 own data in callback functions. The pci field is used when the patch 38 needs to check the PCI subsystem IDs, so on. For non-PCI system, it 39 doesn't have to be set, of course. 40 The modelname field specifies the board's specific configuration. The 41 string is passed to the codec parser, and it depends on the parser how 42 the string is used. 43 These fields, private_data, pci and modelname are all optional. 44 45 The ops field contains the callback functions as the following: 46 47 struct hda_bus_ops { 48 int (*command)(struct hda_codec *codec, hda_nid_t nid, int direct, 49 unsigned int verb, unsigned int parm); 50 unsigned int (*get_response)(struct hda_codec *codec); 51 void (*private_free)(struct hda_bus *); 52 #ifdef CONFIG_SND_HDA_POWER_SAVE 53 void (*pm_notify)(struct hda_codec *codec); 54 #endif 55 }; 56 57 The command callback is called when the codec module needs to send a 58 VERB to the controller. It's always a single command. 59 The get_response callback is called when the codec requires the answer 60 for the last command. These two callbacks are mandatory and have to 61 be given. 62 The third, private_free callback, is optional. It's called in the 63 destructor to release any necessary data in the lowlevel driver. 64 65 The pm_notify callback is available only with 66 CONFIG_SND_HDA_POWER_SAVE kconfig. It's called when the codec needs 67 to power up or may power down. The controller should check the all 68 belonging codecs on the bus whether they are actually powered off 69 (check codec->power_on), and optionally the driver may power down the 70 controller side, too. 71 72 The bus instance is created via snd_hda_bus_new(). You need to pass 73 the card instance, the template, and the pointer to store the 74 resultant bus instance. 75 76 int snd_hda_bus_new(struct snd_card *card, const struct hda_bus_template *temp, 77 struct hda_bus **busp); 78 79 It returns zero if successful. A negative return value means any 80 error during creation. 81 82 83 Creation of Codec Instance 84 ========================== 85 86 Each codec chip on the board is then created on the BUS instance. 87 To create a codec instance, call snd_hda_codec_new(). 88 89 int snd_hda_codec_new(struct hda_bus *bus, unsigned int codec_addr, 90 struct hda_codec **codecp); 91 92 The first argument is the BUS instance, the second argument is the 93 address of the codec, and the last one is the pointer to store the 94 resultant codec instance (can be NULL if not needed). 95 96 The codec is stored in a linked list of bus instance. You can follow 97 the codec list like: 98 99 struct hda_codec *codec; 100 list_for_each_entry(codec, &bus->codec_list, list) { 101 ... 102 } 103 104 The codec isn't initialized at this stage properly. The 105 initialization sequence is called when the controls are built later. 106 107 108 Codec Access 109 ============ 110 111 To access codec, use snd_hda_codec_read() and snd_hda_codec_write(). 112 snd_hda_param_read() is for reading parameters. 113 For writing a sequence of verbs, use snd_hda_sequence_write(). 114 115 There are variants of cached read/write, snd_hda_codec_write_cache(), 116 snd_hda_sequence_write_cache(). These are used for recording the 117 register states for the power-management resume. When no PM is needed, 118 these are equivalent with non-cached version. 119 120 To retrieve the number of sub nodes connected to the given node, use 121 snd_hda_get_sub_nodes(). The connection list can be obtained via 122 snd_hda_get_connections() call. 123 124 When an unsolicited event happens, pass the event via 125 snd_hda_queue_unsol_event() so that the codec routines will process it 126 later. 127 128 129 (Mixer) Controls 130 ================ 131 132 To create mixer controls of all codecs, call 133 snd_hda_build_controls(). It then builds the mixers and does 134 initialization stuff on each codec. 135 136 137 PCM Stuff 138 ========= 139 140 snd_hda_build_pcms() gives the necessary information to create PCM 141 streams. When it's called, each codec belonging to the bus stores 142 codec->num_pcms and codec->pcm_info fields. The num_pcms indicates 143 the number of elements in pcm_info array. The card driver is supposed 144 to traverse the codec linked list, read the pcm information in 145 pcm_info array, and build pcm instances according to them. 146 147 The pcm_info array contains the following record: 148 149 /* PCM information for each substream */ 150 struct hda_pcm_stream { 151 unsigned int substreams; /* number of substreams, 0 = not exist */ 152 unsigned int channels_min; /* min. number of channels */ 153 unsigned int channels_max; /* max. number of channels */ 154 hda_nid_t nid; /* default NID to query rates/formats/bps, or set up */ 155 u32 rates; /* supported rates */ 156 u64 formats; /* supported formats (SNDRV_PCM_FMTBIT_) */ 157 unsigned int maxbps; /* supported max. bit per sample */ 158 struct hda_pcm_ops ops; 159 }; 160 161 /* for PCM creation */ 162 struct hda_pcm { 163 char *name; 164 struct hda_pcm_stream stream[2]; 165 }; 166 167 The name can be passed to snd_pcm_new(). The stream field contains 168 the information for playback (SNDRV_PCM_STREAM_PLAYBACK = 0) and 169 capture (SNDRV_PCM_STREAM_CAPTURE = 1) directions. The card driver 170 should pass substreams to snd_pcm_new() for the number of substreams 171 to create. 172 173 The channels_min, channels_max, rates and formats should be copied to 174 runtime->hw record. They and maxbps fields are used also to compute 175 the format value for the HDA codec and controller. Call 176 snd_hda_calc_stream_format() to get the format value. 177 178 The ops field contains the following callback functions: 179 180 struct hda_pcm_ops { 181 int (*open)(struct hda_pcm_stream *info, struct hda_codec *codec, 182 struct snd_pcm_substream *substream); 183 int (*close)(struct hda_pcm_stream *info, struct hda_codec *codec, 184 struct snd_pcm_substream *substream); 185 int (*prepare)(struct hda_pcm_stream *info, struct hda_codec *codec, 186 unsigned int stream_tag, unsigned int format, 187 struct snd_pcm_substream *substream); 188 int (*cleanup)(struct hda_pcm_stream *info, struct hda_codec *codec, 189 struct snd_pcm_substream *substream); 190 }; 191 192 All are non-NULL, so you can call them safely without NULL check. 193 194 The open callback should be called in PCM open after runtime->hw is 195 set up. It may override some setting and constraints additionally. 196 Similarly, the close callback should be called in the PCM close. 197 198 The prepare callback should be called in PCM prepare. This will set 199 up the codec chip properly for the operation. The cleanup should be 200 called in hw_free to clean up the configuration. 201 202 The caller should check the return value, at least for open and 203 prepare callbacks. When a negative value is returned, some error 204 occurred. 205 206 207 Proc Files 208 ========== 209 210 Each codec dumps the widget node information in 211 /proc/asound/card*/codec#* file. This information would be really 212 helpful for debugging. Please provide its contents together with the 213 bug report. 214 215 216 Power Management 217 ================ 218 219 It's simple: 220 Call snd_hda_suspend() in the PM suspend callback. 221 Call snd_hda_resume() in the PM resume callback. 222 223 224 Codec Preset (Patch) 225 ==================== 226 227 To set up and handle the codec functionality fully, each codec may 228 have a codec preset (patch). It's defined in struct hda_codec_preset: 229 230 struct hda_codec_preset { 231 unsigned int id; 232 unsigned int mask; 233 unsigned int subs; 234 unsigned int subs_mask; 235 unsigned int rev; 236 const char *name; 237 int (*patch)(struct hda_codec *codec); 238 }; 239 240 When the codec id and codec subsystem id match with the given id and 241 subs fields bitwise (with bitmask mask and subs_mask), the callback 242 patch is called. The patch callback should initialize the codec and 243 set the codec->patch_ops field. This is defined as below: 244 245 struct hda_codec_ops { 246 int (*build_controls)(struct hda_codec *codec); 247 int (*build_pcms)(struct hda_codec *codec); 248 int (*init)(struct hda_codec *codec); 249 void (*free)(struct hda_codec *codec); 250 void (*unsol_event)(struct hda_codec *codec, unsigned int res); 251 #ifdef CONFIG_PM 252 int (*suspend)(struct hda_codec *codec, pm_message_t state); 253 int (*resume)(struct hda_codec *codec); 254 #endif 255 #ifdef CONFIG_SND_HDA_POWER_SAVE 256 int (*check_power_status)(struct hda_codec *codec, 257 hda_nid_t nid); 258 #endif 259 }; 260 261 The build_controls callback is called from snd_hda_build_controls(). 262 Similarly, the build_pcms callback is called from 263 snd_hda_build_pcms(). The init callback is called after 264 build_controls to initialize the hardware. 265 The free callback is called as a destructor. 266 267 The unsol_event callback is called when an unsolicited event is 268 received. 269 270 The suspend and resume callbacks are for power management. 271 They can be NULL if no special sequence is required. When the resume 272 callback is NULL, the driver calls the init callback and resumes the 273 registers from the cache. If other handling is needed, you'd need to 274 write your own resume callback. There, the amp values can be resumed 275 via 276 void snd_hda_codec_resume_amp(struct hda_codec *codec); 277 and the other codec registers via 278 void snd_hda_codec_resume_cache(struct hda_codec *codec); 279 280 The check_power_status callback is called when the amp value of the 281 given widget NID is changed. The codec code can turn on/off the power 282 appropriately from this information. 283 284 Each entry can be NULL if not necessary to be called. 285 286 287 Generic Parser 288 ============== 289 290 When the device doesn't match with any given presets, the widgets are 291 parsed via th generic parser (hda_generic.c). Its support is 292 limited: no multi-channel support, for example. 293 294 295 Digital I/O 296 =========== 297 298 Call snd_hda_create_spdif_out_ctls() from the patch to create controls 299 related with SPDIF out. 300 301 302 Helper Functions 303 ================ 304 305 snd_hda_get_codec_name() stores the codec name on the given string. 306 307 snd_hda_check_board_config() can be used to obtain the configuration 308 information matching with the device. Define the model string table 309 and the table with struct snd_pci_quirk entries (zero-terminated), 310 and pass it to the function. The function checks the modelname given 311 as a module parameter, and PCI subsystem IDs. If the matching entry 312 is found, it returns the config field value. 313 314 snd_hda_add_new_ctls() can be used to create and add control entries. 315 Pass the zero-terminated array of struct snd_kcontrol_new 316 317 Macros HDA_CODEC_VOLUME(), HDA_CODEC_MUTE() and their variables can be 318 used for the entry of struct snd_kcontrol_new. 319 320 The input MUX helper callbacks for such a control are provided, too: 321 snd_hda_input_mux_info() and snd_hda_input_mux_put(). See 322 patch_realtek.c for example.