linux/Documentation/sound/alsa/hda_codec.txt
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   1Notes on Universal Interface for Intel High Definition Audio Codec
   2------------------------------------------------------------------
   3
   4Takashi Iwai <tiwai@suse.de>
   5
   6
   7[Still a draft version]
   8
   9
  10General
  11=======
  12
  13The snd-hda-codec module supports the generic access function for the
  14High Definition (HD) audio codecs.  It's designed to be independent
  15from the controller code like ac97 codec module.  The real accessors
  16from/to the controller must be implemented in the lowlevel driver.
  17
  18The structure of this module is similar with ac97_codec module.
  19Each codec chip belongs to a bus class which communicates with the
  20controller.
  21
  22
  23Initialization of Bus Instance
  24==============================
  25
  26The card driver has to create struct hda_bus at first.  The template
  27struct should be filled and passed to the constructor:
  28
  29struct hda_bus_template {
  30        void *private_data;
  31        struct pci_dev *pci;
  32        const char *modelname;
  33        struct hda_bus_ops ops;
  34};
  35
  36The card driver can set and use the private_data field to retrieve its
  37own data in callback functions.  The pci field is used when the patch
  38needs to check the PCI subsystem IDs, so on.  For non-PCI system, it
  39doesn't have to be set, of course.
  40The modelname field specifies the board's specific configuration.  The
  41string is passed to the codec parser, and it depends on the parser how
  42the string is used.
  43These fields, private_data, pci and modelname are all optional.
  44
  45The ops field contains the callback functions as the following:
  46
  47struct 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
  57The command callback is called when the codec module needs to send a
  58VERB to the controller.  It's always a single command.
  59The get_response callback is called when the codec requires the answer
  60for the last command.  These two callbacks are mandatory and have to
  61be given.
  62The third, private_free callback, is optional.  It's called in the
  63destructor to release any necessary data in the lowlevel driver.
  64
  65The pm_notify callback is available only with
  66CONFIG_SND_HDA_POWER_SAVE kconfig.  It's called when the codec needs
  67to power up or may power down.  The controller should check the all
  68belonging codecs on the bus whether they are actually powered off
  69(check codec->power_on), and optionally the driver may power down the
  70controller side, too.
  71
  72The bus instance is created via snd_hda_bus_new().  You need to pass
  73the card instance, the template, and the pointer to store the
  74resultant bus instance.
  75
  76int snd_hda_bus_new(struct snd_card *card, const struct hda_bus_template *temp,
  77                    struct hda_bus **busp);
  78
  79It returns zero if successful.  A negative return value means any
  80error during creation.
  81
  82
  83Creation of Codec Instance
  84==========================
  85
  86Each codec chip on the board is then created on the BUS instance.
  87To create a codec instance, call snd_hda_codec_new().
  88
  89int snd_hda_codec_new(struct hda_bus *bus, unsigned int codec_addr,
  90                      struct hda_codec **codecp);
  91
  92The first argument is the BUS instance, the second argument is the
  93address of the codec, and the last one is the pointer to store the
  94resultant codec instance (can be NULL if not needed).
  95
  96The codec is stored in a linked list of bus instance.  You can follow
  97the codec list like:
  98
  99        struct hda_codec *codec;
 100        list_for_each_entry(codec, &bus->codec_list, list) {
 101                ...
 102        }
 103
 104The codec isn't initialized at this stage properly.  The
 105initialization sequence is called when the controls are built later.
 106
 107
 108Codec Access
 109============
 110
 111To access codec, use snd_hda_codec_read() and snd_hda_codec_write().
 112snd_hda_param_read() is for reading parameters.
 113For writing a sequence of verbs, use snd_hda_sequence_write().
 114
 115There are variants of cached read/write, snd_hda_codec_write_cache(),
 116snd_hda_sequence_write_cache().  These are used for recording the
 117register states for the power-management resume.  When no PM is needed,
 118these are equivalent with non-cached version.
 119
 120To retrieve the number of sub nodes connected to the given node, use
 121snd_hda_get_sub_nodes().  The connection list can be obtained via
 122snd_hda_get_connections() call.
 123
 124When an unsolicited event happens, pass the event via
 125snd_hda_queue_unsol_event() so that the codec routines will process it
 126later.
 127
 128
 129(Mixer) Controls
 130================
 131
 132To create mixer controls of all codecs, call
 133snd_hda_build_controls().  It then builds the mixers and does
 134initialization stuff on each codec.
 135
 136
 137PCM Stuff
 138=========
 139
 140snd_hda_build_pcms() gives the necessary information to create PCM
 141streams.  When it's called, each codec belonging to the bus stores 
 142codec->num_pcms and codec->pcm_info fields.  The num_pcms indicates
 143the number of elements in pcm_info array.  The card driver is supposed
 144to traverse the codec linked list, read the pcm information in
 145pcm_info array, and build pcm instances according to them. 
 146
 147The pcm_info array contains the following record:
 148
 149/* PCM information for each substream */
 150struct 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 */
 162struct hda_pcm {
 163        char *name;
 164        struct hda_pcm_stream stream[2];
 165};
 166
 167The name can be passed to snd_pcm_new().  The stream field contains
 168the information  for playback (SNDRV_PCM_STREAM_PLAYBACK = 0) and
 169capture (SNDRV_PCM_STREAM_CAPTURE = 1) directions.  The card driver
 170should pass substreams to snd_pcm_new() for the number of substreams
 171to create.
 172
 173The channels_min, channels_max, rates and formats should be copied to
 174runtime->hw record.  They and maxbps fields are used also to compute
 175the format value for the HDA codec and controller.  Call
 176snd_hda_calc_stream_format() to get the format value.
 177
 178The ops field contains the following callback functions:
 179
 180struct 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
 192All are non-NULL, so you can call them safely without NULL check.
 193
 194The open callback should be called in PCM open after runtime->hw is
 195set up.  It may override some setting and constraints additionally.
 196Similarly, the close callback should be called in the PCM close.
 197
 198The prepare callback should be called in PCM prepare.  This will set
 199up the codec chip properly for the operation.  The cleanup should be
 200called in hw_free to clean up the configuration.
 201
 202The caller should check the return value, at least for open and
 203prepare callbacks.  When a negative value is returned, some error
 204occurred.
 205
 206
 207Proc Files
 208==========
 209
 210Each codec dumps the widget node information in
 211/proc/asound/card*/codec#* file.  This information would be really
 212helpful for debugging.  Please provide its contents together with the
 213bug report.
 214
 215
 216Power Management
 217================
 218
 219It's simple:
 220Call snd_hda_suspend() in the PM suspend callback.
 221Call snd_hda_resume() in the PM resume callback.
 222
 223
 224Codec Preset (Patch)
 225====================
 226
 227To set up and handle the codec functionality fully, each codec may
 228have 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
 240When the codec id and codec subsystem id match with the given id and
 241subs fields bitwise (with bitmask mask and subs_mask), the callback
 242patch is called.  The patch callback should initialize the codec and
 243set 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
 261The build_controls callback is called from snd_hda_build_controls().
 262Similarly, the build_pcms callback is called from
 263snd_hda_build_pcms().  The init callback is called after
 264build_controls to initialize the hardware.
 265The free callback is called as a destructor.
 266
 267The unsol_event callback is called when an unsolicited event is
 268received.
 269
 270The suspend and resume callbacks are for power management.
 271They can be NULL if no special sequence is required.  When the resume
 272callback is NULL, the driver calls the init callback and resumes the
 273registers from the cache.  If other handling is needed, you'd need to
 274write your own resume callback.  There, the amp values can be resumed
 275via
 276        void snd_hda_codec_resume_amp(struct hda_codec *codec);
 277and the other codec registers via
 278        void snd_hda_codec_resume_cache(struct hda_codec *codec);
 279
 280The check_power_status callback is called when the amp value of the
 281given widget NID is changed.  The codec code can turn on/off the power
 282appropriately from this information.
 283
 284Each entry can be NULL if not necessary to be called.
 285
 286
 287Generic Parser
 288==============
 289
 290When the device doesn't match with any given presets, the widgets are
 291parsed via th generic parser (hda_generic.c).  Its support is
 292limited: no multi-channel support, for example.
 293
 294
 295Digital I/O
 296===========
 297
 298Call snd_hda_create_spdif_out_ctls() from the patch to create controls
 299related with SPDIF out.
 300
 301
 302Helper Functions
 303================
 304
 305snd_hda_get_codec_name() stores the codec name on the given string.
 306
 307snd_hda_check_board_config() can be used to obtain the configuration
 308information matching with the device.  Define the model string table
 309and the table with struct snd_pci_quirk entries (zero-terminated),
 310and pass it to the function.  The function checks the modelname given
 311as a module parameter, and PCI subsystem IDs.  If the matching entry
 312is found, it returns the config field value.
 313
 314snd_hda_add_new_ctls() can be used to create and add control entries.
 315Pass the zero-terminated array of struct snd_kcontrol_new
 316
 317Macros HDA_CODEC_VOLUME(), HDA_CODEC_MUTE() and their variables can be
 318used for the entry of struct snd_kcontrol_new.
 319
 320The input MUX helper callbacks for such a control are provided, too:
 321snd_hda_input_mux_info() and snd_hda_input_mux_put().  See
 322patch_realtek.c for example.
 323