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-Notes on Universal Interface for Intel High Definition Audio Codec
-------------------------------------------------------------------
-
-Takashi Iwai <tiwai@suse.de>
-
-
-[Still a draft version]
-
-
-General
-=======
-
-The snd-hda-codec module supports the generic access function for the
-High Definition (HD) audio codecs. It's designed to be independent
-from the controller code like ac97 codec module. The real accessors
-from/to the controller must be implemented in the lowlevel driver.
-
-The structure of this module is similar with ac97_codec module.
-Each codec chip belongs to a bus class which communicates with the
-controller.
-
-
-Initialization of Bus Instance
-==============================
-
-The card driver has to create struct hda_bus at first. The template
-struct should be filled and passed to the constructor:
-
-struct hda_bus_template {
- void *private_data;
- struct pci_dev *pci;
- const char *modelname;
- struct hda_bus_ops ops;
-};
-
-The card driver can set and use the private_data field to retrieve its
-own data in callback functions. The pci field is used when the patch
-needs to check the PCI subsystem IDs, so on. For non-PCI system, it
-doesn't have to be set, of course.
-The modelname field specifies the board's specific configuration. The
-string is passed to the codec parser, and it depends on the parser how
-the string is used.
-These fields, private_data, pci and modelname are all optional.
-
-The ops field contains the callback functions as the following:
-
-struct hda_bus_ops {
- int (*command)(struct hda_codec *codec, hda_nid_t nid, int direct,
- unsigned int verb, unsigned int parm);
- unsigned int (*get_response)(struct hda_codec *codec);
- void (*private_free)(struct hda_bus *);
-#ifdef CONFIG_SND_HDA_POWER_SAVE
- void (*pm_notify)(struct hda_codec *codec);
-#endif
-};
-
-The command callback is called when the codec module needs to send a
-VERB to the controller. It's always a single command.
-The get_response callback is called when the codec requires the answer
-for the last command. These two callbacks are mandatory and have to
-be given.
-The third, private_free callback, is optional. It's called in the
-destructor to release any necessary data in the lowlevel driver.
-
-The pm_notify callback is available only with
-CONFIG_SND_HDA_POWER_SAVE kconfig. It's called when the codec needs
-to power up or may power down. The controller should check the all
-belonging codecs on the bus whether they are actually powered off
-(check codec->power_on), and optionally the driver may power down the
-controller side, too.
-
-The bus instance is created via snd_hda_bus_new(). You need to pass
-the card instance, the template, and the pointer to store the
-resultant bus instance.
-
-int snd_hda_bus_new(struct snd_card *card, const struct hda_bus_template *temp,
- struct hda_bus **busp);
-
-It returns zero if successful. A negative return value means any
-error during creation.
-
-
-Creation of Codec Instance
-==========================
-
-Each codec chip on the board is then created on the BUS instance.
-To create a codec instance, call snd_hda_codec_new().
-
-int snd_hda_codec_new(struct hda_bus *bus, unsigned int codec_addr,
- struct hda_codec **codecp);
-
-The first argument is the BUS instance, the second argument is the
-address of the codec, and the last one is the pointer to store the
-resultant codec instance (can be NULL if not needed).
-
-The codec is stored in a linked list of bus instance. You can follow
-the codec list like:
-
- struct hda_codec *codec;
- list_for_each_entry(codec, &bus->codec_list, list) {
- ...
- }
-
-The codec isn't initialized at this stage properly. The
-initialization sequence is called when the controls are built later.
-
-
-Codec Access
-============
-
-To access codec, use snd_hda_codec_read() and snd_hda_codec_write().
-snd_hda_param_read() is for reading parameters.
-For writing a sequence of verbs, use snd_hda_sequence_write().
-
-There are variants of cached read/write, snd_hda_codec_write_cache(),
-snd_hda_sequence_write_cache(). These are used for recording the
-register states for the power-management resume. When no PM is needed,
-these are equivalent with non-cached version.
-
-To retrieve the number of sub nodes connected to the given node, use
-snd_hda_get_sub_nodes(). The connection list can be obtained via
-snd_hda_get_connections() call.
-
-When an unsolicited event happens, pass the event via
-snd_hda_queue_unsol_event() so that the codec routines will process it
-later.
-
-
-(Mixer) Controls
-================
-
-To create mixer controls of all codecs, call
-snd_hda_build_controls(). It then builds the mixers and does
-initialization stuff on each codec.
-
-
-PCM Stuff
-=========
-
-snd_hda_build_pcms() gives the necessary information to create PCM
-streams. When it's called, each codec belonging to the bus stores
-codec->num_pcms and codec->pcm_info fields. The num_pcms indicates
-the number of elements in pcm_info array. The card driver is supposed
-to traverse the codec linked list, read the pcm information in
-pcm_info array, and build pcm instances according to them.
-
-The pcm_info array contains the following record:
-
-/* PCM information for each substream */
-struct hda_pcm_stream {
- unsigned int substreams; /* number of substreams, 0 = not exist */
- unsigned int channels_min; /* min. number of channels */
- unsigned int channels_max; /* max. number of channels */
- hda_nid_t nid; /* default NID to query rates/formats/bps, or set up */
- u32 rates; /* supported rates */
- u64 formats; /* supported formats (SNDRV_PCM_FMTBIT_) */
- unsigned int maxbps; /* supported max. bit per sample */
- struct hda_pcm_ops ops;
-};
-
-/* for PCM creation */
-struct hda_pcm {
- char *name;
- struct hda_pcm_stream stream[2];
-};
-
-The name can be passed to snd_pcm_new(). The stream field contains
-the information for playback (SNDRV_PCM_STREAM_PLAYBACK = 0) and
-capture (SNDRV_PCM_STREAM_CAPTURE = 1) directions. The card driver
-should pass substreams to snd_pcm_new() for the number of substreams
-to create.
-
-The channels_min, channels_max, rates and formats should be copied to
-runtime->hw record. They and maxbps fields are used also to compute
-the format value for the HDA codec and controller. Call
-snd_hda_calc_stream_format() to get the format value.
-
-The ops field contains the following callback functions:
-
-struct hda_pcm_ops {
- int (*open)(struct hda_pcm_stream *info, struct hda_codec *codec,
- struct snd_pcm_substream *substream);
- int (*close)(struct hda_pcm_stream *info, struct hda_codec *codec,
- struct snd_pcm_substream *substream);
- int (*prepare)(struct hda_pcm_stream *info, struct hda_codec *codec,
- unsigned int stream_tag, unsigned int format,
- struct snd_pcm_substream *substream);
- int (*cleanup)(struct hda_pcm_stream *info, struct hda_codec *codec,
- struct snd_pcm_substream *substream);
-};
-
-All are non-NULL, so you can call them safely without NULL check.
-
-The open callback should be called in PCM open after runtime->hw is
-set up. It may override some setting and constraints additionally.
-Similarly, the close callback should be called in the PCM close.
-
-The prepare callback should be called in PCM prepare. This will set
-up the codec chip properly for the operation. The cleanup should be
-called in hw_free to clean up the configuration.
-
-The caller should check the return value, at least for open and
-prepare callbacks. When a negative value is returned, some error
-occurred.
-
-
-Proc Files
-==========
-
-Each codec dumps the widget node information in
-/proc/asound/card*/codec#* file. This information would be really
-helpful for debugging. Please provide its contents together with the
-bug report.
-
-
-Power Management
-================
-
-It's simple:
-Call snd_hda_suspend() in the PM suspend callback.
-Call snd_hda_resume() in the PM resume callback.
-
-
-Codec Preset (Patch)
-====================
-
-To set up and handle the codec functionality fully, each codec may
-have a codec preset (patch). It's defined in struct hda_codec_preset:
-
- struct hda_codec_preset {
- unsigned int id;
- unsigned int mask;
- unsigned int subs;
- unsigned int subs_mask;
- unsigned int rev;
- const char *name;
- int (*patch)(struct hda_codec *codec);
- };
-
-When the codec id and codec subsystem id match with the given id and
-subs fields bitwise (with bitmask mask and subs_mask), the callback
-patch is called. The patch callback should initialize the codec and
-set the codec->patch_ops field. This is defined as below:
-
- struct hda_codec_ops {
- int (*build_controls)(struct hda_codec *codec);
- int (*build_pcms)(struct hda_codec *codec);
- int (*init)(struct hda_codec *codec);
- void (*free)(struct hda_codec *codec);
- void (*unsol_event)(struct hda_codec *codec, unsigned int res);
- #ifdef CONFIG_PM
- int (*suspend)(struct hda_codec *codec, pm_message_t state);
- int (*resume)(struct hda_codec *codec);
- #endif
- #ifdef CONFIG_SND_HDA_POWER_SAVE
- int (*check_power_status)(struct hda_codec *codec,
- hda_nid_t nid);
- #endif
- };
-
-The build_controls callback is called from snd_hda_build_controls().
-Similarly, the build_pcms callback is called from
-snd_hda_build_pcms(). The init callback is called after
-build_controls to initialize the hardware.
-The free callback is called as a destructor.
-
-The unsol_event callback is called when an unsolicited event is
-received.
-
-The suspend and resume callbacks are for power management.
-They can be NULL if no special sequence is required. When the resume
-callback is NULL, the driver calls the init callback and resumes the
-registers from the cache. If other handling is needed, you'd need to
-write your own resume callback. There, the amp values can be resumed
-via
- void snd_hda_codec_resume_amp(struct hda_codec *codec);
-and the other codec registers via
- void snd_hda_codec_resume_cache(struct hda_codec *codec);
-
-The check_power_status callback is called when the amp value of the
-given widget NID is changed. The codec code can turn on/off the power
-appropriately from this information.
-
-Each entry can be NULL if not necessary to be called.
-
-
-Generic Parser
-==============
-
-When the device doesn't match with any given presets, the widgets are
-parsed via th generic parser (hda_generic.c). Its support is
-limited: no multi-channel support, for example.
-
-
-Digital I/O
-===========
-
-Call snd_hda_create_spdif_out_ctls() from the patch to create controls
-related with SPDIF out.
-
-
-Helper Functions
-================
-
-snd_hda_get_codec_name() stores the codec name on the given string.
-
-snd_hda_check_board_config() can be used to obtain the configuration
-information matching with the device. Define the model string table
-and the table with struct snd_pci_quirk entries (zero-terminated),
-and pass it to the function. The function checks the modelname given
-as a module parameter, and PCI subsystem IDs. If the matching entry
-is found, it returns the config field value.
-
-snd_hda_add_new_ctls() can be used to create and add control entries.
-Pass the zero-terminated array of struct snd_kcontrol_new
-
-Macros HDA_CODEC_VOLUME(), HDA_CODEC_MUTE() and their variables can be
-used for the entry of struct snd_kcontrol_new.
-
-The input MUX helper callbacks for such a control are provided, too:
-snd_hda_input_mux_info() and snd_hda_input_mux_put(). See
-patch_realtek.c for example.