MORE NOTES ON HD-AUDIO DRIVER
  =============================
  					Takashi Iwai <tiwai@suse.de>
  
  
  GENERAL
  -------
  
  HD-audio is the new standard on-board audio component on modern PCs
  after AC97.  Although Linux has been supporting HD-audio since long
  time ago, there are often problems with new machines.  A part of the
  problem is broken BIOS, and the rest is the driver implementation.
  This document explains the brief trouble-shooting and debugging
  methods for the	HD-audio hardware.
  
  The HD-audio component consists of two parts: the controller chip and 
  the codec chips on the HD-audio bus.  Linux provides a single driver
  for all controllers, snd-hda-intel.  Although the driver name contains
  a word of a well-known hardware vendor, it's not specific to it but for
  all controller chips by other companies.  Since the HD-audio
  controllers are supposed to be compatible, the single snd-hda-driver
  should work in most cases.  But, not surprisingly, there are known
  bugs and issues specific to each controller type.  The snd-hda-intel
  driver has a bunch of workarounds for these as described below.
  
  A controller may have multiple codecs.  Usually you have one audio
  codec and optionally one modem codec.  In theory, there might be
  multiple audio codecs, e.g. for analog and digital outputs, and the
  driver might not work properly because of conflict of mixer elements.
  This should be fixed in future if such hardware really exists.
  
  The snd-hda-intel driver has several different codec parsers depending
  on the codec.  It has a generic parser as a fallback, but this
  functionality is fairly limited until now.  Instead of the generic
  parser, usually the codec-specific parser (coded in patch_*.c) is used
  for the codec-specific implementations.  The details about the
  codec-specific problems are explained in the later sections.
  
  If you are interested in the deep debugging of HD-audio, read the
  HD-audio specification at first.  The specification is found on
  Intel's web page, for example:
  
  - http://www.intel.com/standards/hdaudio/
  
  
  HD-AUDIO CONTROLLER
  -------------------
  
  DMA-Position Problem
  ~~~~~~~~~~~~~~~~~~~~
  The most common problem of the controller is the inaccurate DMA
  pointer reporting.  The DMA pointer for playback and capture can be
  read in two ways, either via a LPIB register or via a position-buffer
  map.  As default the driver tries to read from the io-mapped
  position-buffer, and falls back to LPIB if the position-buffer appears
  dead.  However, this detection isn't perfect on some devices.  In such
  a case, you can change the default method via `position_fix` option.
  
  `position_fix=1` means to use LPIB method explicitly.
  `position_fix=2` means to use the position-buffer.
  `position_fix=3` means to use a combination of both methods, needed
  for some VIA controllers.  The capture stream position is corrected
  by comparing both LPIB and position-buffer values.
  `position_fix=4` is another combination available for all controllers,
  and uses LPIB for the playback and the position-buffer for the capture
  streams.
  0 is the default value for all other
  controllers, the automatic check and fallback to LPIB as described in
  the above.  If you get a problem of repeated sounds, this option might
  help.
  
  In addition to that, every controller is known to be broken regarding
  the wake-up timing.  It wakes up a few samples before actually
  processing the data on the buffer.  This caused a lot of problems, for
  example, with ALSA dmix or JACK.  Since 2.6.27 kernel, the driver puts
  an artificial delay to the wake up timing.  This delay is controlled
  via `bdl_pos_adj` option. 
  
  When `bdl_pos_adj` is a negative value (as default), it's assigned to
  an appropriate value depending on the controller chip.  For Intel
  chips, it'd be 1 while it'd be 32 for others.  Usually this works.
  Only in case it doesn't work and you get warning messages, you should
  change this parameter to other values.
  
  
  Codec-Probing Problem
  ~~~~~~~~~~~~~~~~~~~~~
  A less often but a more severe problem is the codec probing.  When
  BIOS reports the available codec slots wrongly, the driver gets
  confused and tries to access the non-existing codec slot.  This often
  results in the total screw-up, and destructs the further communication
  with the codec chips.  The symptom appears usually as error messages
  like:
  ------------------------------------------------------------------------
    hda_intel: azx_get_response timeout, switching to polling mode:
          last cmd=0x12345678
    hda_intel: azx_get_response timeout, switching to single_cmd mode:
          last cmd=0x12345678
  ------------------------------------------------------------------------
  
  The first line is a warning, and this is usually relatively harmless.
  It means that the codec response isn't notified via an IRQ.  The
  driver uses explicit polling method to read the response.  It gives
  very slight CPU overhead, but you'd unlikely notice it.
  
  The second line is, however, a fatal error.  If this happens, usually
  it means that something is really wrong.  Most likely you are
  accessing a non-existing codec slot.
  
  Thus, if the second error message appears, try to narrow the probed
  codec slots via `probe_mask` option.  It's a bitmask, and each bit
  corresponds to the codec slot.  For example, to probe only the first
  slot, pass `probe_mask=1`.  For the first and the third slots, pass
  `probe_mask=5` (where 5 = 1 | 4), and so on.
  
  Since 2.6.29 kernel, the driver has a more robust probing method, so
  this error might happen rarely, though.
  
  On a machine with a broken BIOS, sometimes you need to force the
  driver to probe the codec slots the hardware doesn't report for use.
  In such a case, turn the bit 8 (0x100) of `probe_mask` option on.
  Then the rest 8 bits are passed as the codec slots to probe
  unconditionally.  For example, `probe_mask=0x103` will force to probe
  the codec slots 0 and 1 no matter what the hardware reports.
  
  
  Interrupt Handling
  ~~~~~~~~~~~~~~~~~~
  HD-audio driver uses MSI as default (if available) since 2.6.33
  kernel as MSI works better on some machines, and in general, it's
  better for performance.  However, Nvidia controllers showed bad
  regressions with MSI (especially in a combination with AMD chipset),
  thus we disabled MSI for them.
  
  There seem also still other devices that don't work with MSI.  If you
  see a regression wrt the sound quality (stuttering, etc) or a lock-up
  in the recent kernel, try to pass `enable_msi=0` option to disable
  MSI.  If it works, you can add the known bad device to the blacklist
  defined in hda_intel.c.  In such a case, please report and give the
  patch back to the upstream developer. 
  
  
  HD-AUDIO CODEC
  --------------
  
  Model Option
  ~~~~~~~~~~~~
  The most common problem regarding the HD-audio driver is the
  unsupported codec features or the mismatched device configuration.
  Most of codec-specific code has several preset models, either to
  override the BIOS setup or to provide more comprehensive features.
  
  The driver checks PCI SSID and looks through the static configuration
  table until any matching entry is found.  If you have a new machine,
  you may see a message like below:
  ------------------------------------------------------------------------
      hda_codec: ALC880: BIOS auto-probing.
  ------------------------------------------------------------------------
  Meanwhile, in the earlier versions, you would see a message like:
  ------------------------------------------------------------------------
      hda_codec: Unknown model for ALC880, trying auto-probe from BIOS...
  ------------------------------------------------------------------------
  Even if you see such a message, DON'T PANIC.  Take a deep breath and
  keep your towel.  First of all, it's an informational message, no
  warning, no error.  This means that the PCI SSID of your device isn't
  listed in the known preset model (white-)list.  But, this doesn't mean
  that the driver is broken.  Many codec-drivers provide the automatic
  configuration mechanism based on the BIOS setup.
  
  The HD-audio codec has usually "pin" widgets, and BIOS sets the default
  configuration of each pin, which indicates the location, the
  connection type, the jack color, etc.  The HD-audio driver can guess
  the right connection judging from these default configuration values.
  However -- some codec-support codes, such as patch_analog.c, don't
  support the automatic probing (yet as of 2.6.28).  And, BIOS is often,
  yes, pretty often broken.  It sets up wrong values and screws up the
  driver.
  
  The preset model (or recently called as "fix-up") is provided
  basically to overcome such a situation.  When the matching preset
  model is found in the white-list, the driver assumes the static
  configuration of that preset with the correct pin setup, etc.
  Thus, if you have a newer machine with a slightly different PCI SSID
  (or codec SSID) from the existing one, you may have a good chance to
  re-use the same model.  You can pass the `model` option to specify the
  preset model instead of PCI (and codec-) SSID look-up.
  
  What `model` option values are available depends on the codec chip.
  Check your codec chip from the codec proc file (see "Codec Proc-File"
  section below).  It will show the vendor/product name of your codec
  chip.  Then, see Documentation/sound/alsa/HD-Audio-Models.txt file,
  the section of HD-audio driver.  You can find a list of codecs
  and `model` options belonging to each codec.  For example, for Realtek
  ALC262 codec chip, pass `model=ultra` for devices that are compatible
  with Samsung Q1 Ultra.
  
  Thus, the first thing you can do for any brand-new, unsupported and
  non-working HD-audio hardware is to check HD-audio codec and several
  different `model` option values.  If you have any luck, some of them
  might suit with your device well.
  
  There are a few special model option values:
  - when 'nofixup' is passed, the device-specific fixups in the codec
    parser are skipped.
  - when `generic` is passed, the codec-specific parser is skipped and
    only the generic parser is used.
  
  
  Speaker and Headphone Output
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  One of the most frequent (and obvious) bugs with HD-audio is the
  silent output from either or both of a built-in speaker and a
  headphone jack.  In general, you should try a headphone output at
  first.  A speaker output often requires more additional controls like
  the external amplifier bits.  Thus a headphone output has a slightly
  better chance.
  
  Before making a bug report, double-check whether the mixer is set up
  correctly.  The recent version of snd-hda-intel driver provides mostly
  "Master" volume control as well as "Front" volume (where Front
  indicates the front-channels).  In addition, there can be individual
  "Headphone" and "Speaker" controls.
  
  Ditto for the speaker output.  There can be "External Amplifier"
  switch on some codecs.  Turn on this if present.
  
  Another related problem is the automatic mute of speaker output by
  headphone plugging.  This feature is implemented in most cases, but
  not on every preset model or codec-support code.
  
  In anyway, try a different model option if you have such a problem.
  Some other models may match better and give you more matching
  functionality.  If none of the available models works, send a bug
  report.  See the bug report section for details.
  
  If you are masochistic enough to debug the driver problem, note the
  following:
  
  - The speaker (and the headphone, too) output often requires the
    external amplifier.  This can be set usually via EAPD verb or a
    certain GPIO.  If the codec pin supports EAPD, you have a better
    chance via SET_EAPD_BTL verb (0x70c).  On others, GPIO pin (mostly
    it's either GPIO0 or GPIO1) may turn on/off EAPD.
  - Some Realtek codecs require special vendor-specific coefficients to
    turn on the amplifier.  See patch_realtek.c.
  - IDT codecs may have extra power-enable/disable controls on each
    analog pin.  See patch_sigmatel.c.
  - Very rare but some devices don't accept the pin-detection verb until
    triggered.  Issuing GET_PIN_SENSE verb (0xf09) may result in the
    codec-communication stall.  Some examples are found in
    patch_realtek.c.
  
  
  Capture Problems
  ~~~~~~~~~~~~~~~~
  The capture problems are often because of missing setups of mixers.
  Thus, before submitting a bug report, make sure that you set up the
  mixer correctly.  For example, both "Capture Volume" and "Capture
  Switch" have to be set properly in addition to the right "Capture
  Source" or "Input Source" selection.  Some devices have "Mic Boost"
  volume or switch.
  
  When the PCM device is opened via "default" PCM (without pulse-audio
  plugin), you'll likely have "Digital Capture Volume" control as well.
  This is provided for the extra gain/attenuation of the signal in
  software, especially for the inputs without the hardware volume
  control such as digital microphones.  Unless really needed, this
  should be set to exactly 50%, corresponding to 0dB -- neither extra
  gain nor attenuation.  When you use "hw" PCM, i.e., a raw access PCM,
  this control will have no influence, though.
  
  It's known that some codecs / devices have fairly bad analog circuits,
  and the recorded sound contains a certain DC-offset.  This is no bug
  of the driver.
  
  Most of modern laptops have no analog CD-input connection.  Thus, the
  recording from CD input won't work in many cases although the driver
  provides it as the capture source.  Use CDDA instead.
  
  The automatic switching of the built-in and external mic per plugging
  is implemented on some codec models but not on every model.  Partly
  because of my laziness but mostly lack of testers.  Feel free to
  submit the improvement patch to the author.
  
  
  Direct Debugging
  ~~~~~~~~~~~~~~~~
  If no model option gives you a better result, and you are a tough guy
  to fight against evil, try debugging via hitting the raw HD-audio
  codec verbs to the device.  Some tools are available: hda-emu and
  hda-analyzer.  The detailed description is found in the sections
  below.  You'd need to enable hwdep for using these tools.  See "Kernel
  Configuration" section.
  
  
  OTHER ISSUES
  ------------
  
  Kernel Configuration
  ~~~~~~~~~~~~~~~~~~~~
  In general, I recommend you to enable the sound debug option,
  `CONFIG_SND_DEBUG=y`, no matter whether you are debugging or not.
  This enables snd_printd() macro and others, and you'll get additional
  kernel messages at probing.
  
  In addition, you can enable `CONFIG_SND_DEBUG_VERBOSE=y`.  But this
  will give you far more messages.  Thus turn this on only when you are
  sure to want it.
  
  Don't forget to turn on the appropriate `CONFIG_SND_HDA_CODEC_*`
  options.  Note that each of them corresponds to the codec chip, not
  the controller chip.  Thus, even if lspci shows the Nvidia controller,
  you may need to choose the option for other vendors.  If you are
  unsure, just select all yes.
  
  `CONFIG_SND_HDA_HWDEP` is a useful option for debugging the driver.
  When this is enabled, the driver creates hardware-dependent devices
  (one per each codec), and you have a raw access to the device via
  these device files.  For example, `hwC0D2` will be created for the
  codec slot #2 of the first card (#0).  For debug-tools such as
  hda-verb and hda-analyzer, the hwdep device has to be enabled.
  Thus, it'd be better to turn this on always.
  
  `CONFIG_SND_HDA_RECONFIG` is a new option, and this depends on the
  hwdep option above.  When enabled, you'll have some sysfs files under
  the corresponding hwdep directory.  See "HD-audio reconfiguration"
  section below.
  
  `CONFIG_SND_HDA_POWER_SAVE` option enables the power-saving feature.
  See "Power-saving" section below.
  
  
  Codec Proc-File
  ~~~~~~~~~~~~~~~
  The codec proc-file is a treasure-chest for debugging HD-audio.
  It shows most of useful information of each codec widget.
  
  The proc file is located in /proc/asound/card*/codec#*, one file per
  each codec slot.  You can know the codec vendor, product id and
  names, the type of each widget, capabilities and so on.
  This file, however, doesn't show the jack sensing state, so far.  This
  is because the jack-sensing might be depending on the trigger state.
  
  This file will be picked up by the debug tools, and also it can be fed
  to the emulator as the primary codec information.  See the debug tools
  section below.
  
  This proc file can be also used to check whether the generic parser is
  used.  When the generic parser is used, the vendor/product ID name
  will appear as "Realtek ID 0262", instead of "Realtek ALC262".
  
  
  HD-Audio Reconfiguration
  ~~~~~~~~~~~~~~~~~~~~~~~~
  This is an experimental feature to allow you re-configure the HD-audio
  codec dynamically without reloading the driver.  The following sysfs
  files are available under each codec-hwdep device directory (e.g. 
  /sys/class/sound/hwC0D0):
  
  vendor_id::
    Shows the 32bit codec vendor-id hex number.  You can change the
    vendor-id value by writing to this file.
  subsystem_id::
    Shows the 32bit codec subsystem-id hex number.  You can change the
    subsystem-id value by writing to this file.
  revision_id::
    Shows the 32bit codec revision-id hex number.  You can change the
    revision-id value by writing to this file.
  afg::
    Shows the AFG ID.  This is read-only.
  mfg::
    Shows the MFG ID.  This is read-only.
  name::
    Shows the codec name string.  Can be changed by writing to this
    file.
  modelname::
    Shows the currently set `model` option.  Can be changed by writing
    to this file.
  init_verbs::
    The extra verbs to execute at initialization.  You can add a verb by
    writing to this file.  Pass three numbers: nid, verb and parameter
    (separated with a space).
  hints::
    Shows / stores hint strings for codec parsers for any use.
    Its format is `key = value`.  For example, passing `jack_detect = no`
    will disable the jack detection of the machine completely.
  init_pin_configs::
    Shows the initial pin default config values set by BIOS.
  driver_pin_configs::
    Shows the pin default values set by the codec parser explicitly.
    This doesn't show all pin values but only the changed values by
    the parser.  That is, if the parser doesn't change the pin default
    config values by itself, this will contain nothing.
  user_pin_configs::
    Shows the pin default config values to override the BIOS setup.
    Writing this (with two numbers, NID and value) appends the new
    value.  The given will be used instead of the initial BIOS value at
    the next reconfiguration time.  Note that this config will override
    even the driver pin configs, too.
  reconfig::
    Triggers the codec re-configuration.  When any value is written to
    this file, the driver re-initialize and parses the codec tree
    again.  All the changes done by the sysfs entries above are taken
    into account.
  clear::
    Resets the codec, removes the mixer elements and PCM stuff of the
    specified codec, and clear all init verbs and hints.
  
  For example, when you want to change the pin default configuration
  value of the pin widget 0x14 to 0x9993013f, and let the driver
  re-configure based on that state, run like below:
  ------------------------------------------------------------------------
    # echo 0x14 0x9993013f > /sys/class/sound/hwC0D0/user_pin_configs
    # echo 1 > /sys/class/sound/hwC0D0/reconfig  
  ------------------------------------------------------------------------
  
  
  Hint Strings
  ~~~~~~~~~~~~
  The codec parser have several switches and adjustment knobs for
  matching better with the actual codec or device behavior.  Many of
  them can be adjusted dynamically via "hints" strings as mentioned in
  the section above.  For example, by passing `jack_detect = no` string
  via sysfs or a patch file, you can disable the jack detection, thus
  the codec parser will skip the features like auto-mute or mic
  auto-switch.  As a boolean value, either `yes`, `no`, `true`, `false`,
  `1` or `0` can be passed.
  
  The generic parser supports the following hints:
  
  - jack_detect (bool): specify whether the jack detection is available
    at all on this machine; default true
  - inv_jack_detect (bool): indicates that the jack detection logic is
    inverted
  - trigger_sense (bool): indicates that the jack detection needs the
    explicit call of AC_VERB_SET_PIN_SENSE verb
  - inv_eapd (bool): indicates that the EAPD is implemented in the
    inverted logic
  - pcm_format_first (bool): sets the PCM format before the stream tag
    and channel ID
  - sticky_stream (bool): keep the PCM format, stream tag and ID as long
    as possible; default true
  - spdif_status_reset (bool): reset the SPDIF status bits at each time
    the SPDIF stream is set up
  -  pin_amp_workaround (bool): the output pin may have multiple amp
    values
  - single_adc_amp (bool): ADCs can have only single input amps
  - auto_mute (bool): enable/disable the headphone auto-mute feature;
    default true
  - auto_mic (bool): enable/disable the mic auto-switch feature; default
    true
  - line_in_auto_switch (bool): enable/disable the line-in auto-switch
    feature; default false
  - need_dac_fix (bool): limits the DACs depending on the channel count
  - primary_hp (bool): probe headphone jacks as the primary outputs;
    default true
  - multi_io (bool): try probing multi-I/O config (e.g. shared
    line-in/surround, mic/clfe jacks)
  - multi_cap_vol (bool): provide multiple capture volumes
  - inv_dmic_split (bool): provide split internal mic volume/switch for
    phase-inverted digital mics
  - indep_hp (bool): provide the independent headphone PCM stream and
    the corresponding mixer control, if available
  - add_stereo_mix_input (bool): add the stereo mix (analog-loopback
    mix) to the input mux if available
  - add_jack_modes (bool): add "xxx Jack Mode" enum controls to each
    I/O jack for allowing to change the headphone amp and mic bias VREF
    capabilities
  - power_down_unused (bool): power down the unused widgets
  - add_hp_mic (bool): add the headphone to capture source if possible
  - hp_mic_detect (bool): enable/disable the hp/mic shared input for a
    single built-in mic case; default true
  - mixer_nid (int): specifies the widget NID of the analog-loopback
    mixer
  
  
  Early Patching
  ~~~~~~~~~~~~~~
  When CONFIG_SND_HDA_PATCH_LOADER=y is set, you can pass a "patch" as a
  firmware file for modifying the HD-audio setup before initializing the
  codec.  This can work basically like the reconfiguration via sysfs in
  the above, but it does it before the first codec configuration.
  
  A patch file is a plain text file which looks like below:
  
  ------------------------------------------------------------------------
    [codec]
    0x12345678 0xabcd1234 2
  
    [model]
    auto
  
    [pincfg]
    0x12 0x411111f0
  
    [verb]
    0x20 0x500 0x03
    0x20 0x400 0xff
  
    [hint]
    jack_detect = no
  ------------------------------------------------------------------------
  
  The file needs to have a line `[codec]`.  The next line should contain
  three numbers indicating the codec vendor-id (0x12345678 in the
  example), the codec subsystem-id (0xabcd1234) and the address (2) of
  the codec.  The rest patch entries are applied to this specified codec
  until another codec entry is given.  Passing 0 or a negative number to
  the first or the second value will make the check of the corresponding
  field be skipped.  It'll be useful for really broken devices that don't
  initialize SSID properly.
  
  The `[model]` line allows to change the model name of the each codec.
  In the example above, it will be changed to model=auto.
  Note that this overrides the module option.
  
  After the `[pincfg]` line, the contents are parsed as the initial
  default pin-configurations just like `user_pin_configs` sysfs above.
  The values can be shown in user_pin_configs sysfs file, too.
  
  Similarly, the lines after `[verb]` are parsed as `init_verbs`
  sysfs entries, and the lines after `[hint]` are parsed as `hints`
  sysfs entries, respectively.
  
  Another example to override the codec vendor id from 0x12345678 to
  0xdeadbeef is like below:
  ------------------------------------------------------------------------
    [codec]
    0x12345678 0xabcd1234 2
  
    [vendor_id]
    0xdeadbeef
  ------------------------------------------------------------------------
  
  In the similar way, you can override the codec subsystem_id via
  `[subsystem_id]`, the revision id via `[revision_id]` line.
  Also, the codec chip name can be rewritten via `[chip_name]` line.
  ------------------------------------------------------------------------
    [codec]
    0x12345678 0xabcd1234 2
  
    [subsystem_id]
    0xffff1111
  
    [revision_id]
    0x10
  
    [chip_name]
    My-own NEWS-0002
  ------------------------------------------------------------------------
  
  The hd-audio driver reads the file via request_firmware().  Thus,
  a patch file has to be located on the appropriate firmware path,
  typically, /lib/firmware.  For example, when you pass the option
  `patch=hda-init.fw`, the file /lib/firmware/hda-init.fw must be
  present.
  
  The patch module option is specific to each card instance, and you
  need to give one file name for each instance, separated by commas.
  For example, if you have two cards, one for an on-board analog and one 
  for an HDMI video board, you may pass patch option like below:
  ------------------------------------------------------------------------
      options snd-hda-intel patch=on-board-patch,hdmi-patch
  ------------------------------------------------------------------------
  
  
  Power-Saving
  ~~~~~~~~~~~~
  The power-saving is a kind of auto-suspend of the device.  When the
  device is inactive for a certain time, the device is automatically
  turned off to save the power.  The time to go down is specified via
  `power_save` module option, and this option can be changed dynamically
  via sysfs.
  
  The power-saving won't work when the analog loopback is enabled on
  some codecs.  Make sure that you mute all unneeded signal routes when
  you want the power-saving.
  
  The power-saving feature might cause audible click noises at each
  power-down/up depending on the device.  Some of them might be
  solvable, but some are hard, I'm afraid.  Some distros such as
  openSUSE enables the power-saving feature automatically when the power
  cable is unplugged.  Thus, if you hear noises, suspect first the
  power-saving.  See /sys/module/snd_hda_intel/parameters/power_save to
  check the current value.  If it's non-zero, the feature is turned on.
  
  The recent kernel supports the runtime PM for the HD-audio controller
  chip, too.  It means that the HD-audio controller is also powered up /
  down dynamically.  The feature is enabled only for certain controller
  chips like Intel LynxPoint.  You can enable/disable this feature
  forcibly by setting `power_save_controller` option, which is also
  available at /sys/module/snd_hda_intel/parameters directory.
  
  
  Tracepoints
  ~~~~~~~~~~~
  The hd-audio driver gives a few basic tracepoints.
  `hda:hda_send_cmd` traces each CORB write while `hda:hda_get_response`
  traces the response from RIRB (only when read from the codec driver).
  `hda:hda_bus_reset` traces the bus-reset due to fatal error, etc,
  `hda:hda_unsol_event` traces the unsolicited events, and
  `hda:hda_power_down` and `hda:hda_power_up` trace the power down/up
  via power-saving behavior.
  
  Enabling all tracepoints can be done like
  ------------------------------------------------------------------------
    # echo 1 > /sys/kernel/debug/tracing/events/hda/enable
  ------------------------------------------------------------------------
  then after some commands, you can traces from
  /sys/kernel/debug/tracing/trace file.  For example, when you want to
  trace what codec command is sent, enable the tracepoint like:
  ------------------------------------------------------------------------
    # cat /sys/kernel/debug/tracing/trace
    # tracer: nop
    #
    #       TASK-PID    CPU#    TIMESTAMP  FUNCTION
    #          | |       |          |         |
           <...>-7807  [002] 105147.774889: hda_send_cmd: [0:0] val=e3a019
           <...>-7807  [002] 105147.774893: hda_send_cmd: [0:0] val=e39019
           <...>-7807  [002] 105147.999542: hda_send_cmd: [0:0] val=e3a01a
           <...>-7807  [002] 105147.999543: hda_send_cmd: [0:0] val=e3901a
           <...>-26764 [001] 349222.837143: hda_send_cmd: [0:0] val=e3a019
           <...>-26764 [001] 349222.837148: hda_send_cmd: [0:0] val=e39019
           <...>-26764 [001] 349223.058539: hda_send_cmd: [0:0] val=e3a01a
           <...>-26764 [001] 349223.058541: hda_send_cmd: [0:0] val=e3901a
  ------------------------------------------------------------------------
  Here `[0:0]` indicates the card number and the codec address, and
  `val` shows the value sent to the codec, respectively.  The value is
  a packed value, and you can decode it via hda-decode-verb program
  included in hda-emu package below.  For example, the value e3a019 is
  to set the left output-amp value to 25.
  ------------------------------------------------------------------------
    % hda-decode-verb 0xe3a019
    raw value = 0x00e3a019
    cid = 0, nid = 0x0e, verb = 0x3a0, parm = 0x19
    raw value: verb = 0x3a0, parm = 0x19
    verbname = set_amp_gain_mute
    amp raw val = 0xa019
    output, left, idx=0, mute=0, val=25
  ------------------------------------------------------------------------
  
  
  Development Tree
  ~~~~~~~~~~~~~~~~
  The latest development codes for HD-audio are found on sound git tree:
  
  - git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git
  
  The master branch or for-next branches can be used as the main
  development branches in general while the development for the current
  and next kernels are found in for-linus and for-next branches,
  respectively.
  
  If you are using the latest Linus tree, it'd be better to pull the
  above GIT tree onto it.  If you are using the older kernels, an easy
  way to try the latest ALSA code is to build from the snapshot
  tarball.  There are daily tarballs and the latest snapshot tarball.
  All can be built just like normal alsa-driver release packages, that
  is, installed via the usual spells: configure, make and make
  install(-modules).  See INSTALL in the package.  The snapshot tarballs
  are found at:
  
  - ftp://ftp.suse.com/pub/people/tiwai/snapshot/
  
  
  Sending a Bug Report
  ~~~~~~~~~~~~~~~~~~~~
  If any model or module options don't work for your device, it's time
  to send a bug report to the developers.  Give the following in your
  bug report:
  
  - Hardware vendor, product and model names
  - Kernel version (and ALSA-driver version if you built externally)
  - `alsa-info.sh` output; run with `--no-upload` option.  See the
    section below about alsa-info
  
  If it's a regression, at best, send alsa-info outputs of both working
  and non-working kernels.  This is really helpful because we can
  compare the codec registers directly.
  
  Send a bug report either the followings:
  
  kernel-bugzilla::
    https://bugzilla.kernel.org/
  alsa-devel ML::
    alsa-devel@alsa-project.org
  
  
  DEBUG TOOLS
  -----------
  
  This section describes some tools available for debugging HD-audio
  problems.
  
  alsa-info
  ~~~~~~~~~
  The script `alsa-info.sh` is a very useful tool to gather the audio
  device information.  You can fetch the latest version from:
  
  - http://www.alsa-project.org/alsa-info.sh
  
  Run this script as root, and it will gather the important information
  such as the module lists, module parameters, proc file contents
  including the codec proc files, mixer outputs and the control
  elements.  As default, it will store the information onto a web server
  on alsa-project.org.  But, if you send a bug report, it'd be better to
  run with `--no-upload` option, and attach the generated file.
  
  There are some other useful options.  See `--help` option output for
  details.
  
  When a probe error occurs or when the driver obviously assigns a
  mismatched model, it'd be helpful to load the driver with
  `probe_only=1` option (at best after the cold reboot) and run
  alsa-info at this state.  With this option, the driver won't configure
  the mixer and PCM but just tries to probe the codec slot.  After
  probing, the proc file is available, so you can get the raw codec
  information before modified by the driver.  Of course, the driver
  isn't usable with `probe_only=1`.  But you can continue the
  configuration via hwdep sysfs file if hda-reconfig option is enabled.
  Using `probe_only` mask 2 skips the reset of HDA codecs (use
  `probe_only=3` as module option). The hwdep interface can be used
  to determine the BIOS codec initialization.
  
  
  hda-verb
  ~~~~~~~~
  hda-verb is a tiny program that allows you to access the HD-audio
  codec directly.  You can execute a raw HD-audio codec verb with this.
  This program accesses the hwdep device, thus you need to enable the
  kernel config `CONFIG_SND_HDA_HWDEP=y` beforehand.
  
  The hda-verb program takes four arguments: the hwdep device file, the
  widget NID, the verb and the parameter.  When you access to the codec
  on the slot 2 of the card 0, pass /dev/snd/hwC0D2 to the first
  argument, typically.  (However, the real path name depends on the
  system.)
  
  The second parameter is the widget number-id to access.  The third
  parameter can be either a hex/digit number or a string corresponding
  to a verb.  Similarly, the last parameter is the value to write, or
  can be a string for the parameter type.
  
  ------------------------------------------------------------------------
    % hda-verb /dev/snd/hwC0D0 0x12 0x701 2
    nid = 0x12, verb = 0x701, param = 0x2
    value = 0x0
  
    % hda-verb /dev/snd/hwC0D0 0x0 PARAMETERS VENDOR_ID
    nid = 0x0, verb = 0xf00, param = 0x0
    value = 0x10ec0262
  
    % hda-verb /dev/snd/hwC0D0 2 set_a 0xb080
    nid = 0x2, verb = 0x300, param = 0xb080
    value = 0x0
  ------------------------------------------------------------------------
  
  Although you can issue any verbs with this program, the driver state
  won't be always updated.  For example, the volume values are usually
  cached in the driver, and thus changing the widget amp value directly
  via hda-verb won't change the mixer value.
  
  The hda-verb program is included now in alsa-tools:
  
  - git://git.alsa-project.org/alsa-tools.git
  
  Also, the old stand-alone package is found in the ftp directory:
  
  - ftp://ftp.suse.com/pub/people/tiwai/misc/
  
  Also a git repository is available:
  
  - git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/hda-verb.git
  
  See README file in the tarball for more details about hda-verb
  program.
  
  
  hda-analyzer
  ~~~~~~~~~~~~
  hda-analyzer provides a graphical interface to access the raw HD-audio
  control, based on pyGTK2 binding.  It's a more powerful version of
  hda-verb.  The program gives you an easy-to-use GUI stuff for showing
  the widget information and adjusting the amp values, as well as the
  proc-compatible output.
  
  The hda-analyzer:
  
  - http://git.alsa-project.org/?p=alsa.git;a=tree;f=hda-analyzer
  
  is a part of alsa.git repository in alsa-project.org:
  
  - git://git.alsa-project.org/alsa.git
  
  Codecgraph
  ~~~~~~~~~~
  Codecgraph is a utility program to generate a graph and visualizes the
  codec-node connection of a codec chip.  It's especially useful when
  you analyze or debug a codec without a proper datasheet.  The program
  parses the given codec proc file and converts to SVG via graphiz
  program.
  
  The tarball and GIT trees are found in the web page at:
  
  - http://helllabs.org/codecgraph/
  
  
  hda-emu
  ~~~~~~~
  hda-emu is an HD-audio emulator.  The main purpose of this program is
  to debug an HD-audio codec without the real hardware.  Thus, it
  doesn't emulate the behavior with the real audio I/O, but it just
  dumps the codec register changes and the ALSA-driver internal changes
  at probing and operating the HD-audio driver.
  
  The program requires a codec proc-file to simulate.  Get a proc file
  for the target codec beforehand, or pick up an example codec from the
  codec proc collections in the tarball.  Then, run the program with the
  proc file, and the hda-emu program will start parsing the codec file
  and simulates the HD-audio driver:
  
  ------------------------------------------------------------------------
    % hda-emu codecs/stac9200-dell-d820-laptop
    # Parsing..
    hda_codec: Unknown model for STAC9200, using BIOS defaults
    hda_codec: pin nid 08 bios pin config 40c003fa
    ....
  ------------------------------------------------------------------------
  
  The program gives you only a very dumb command-line interface.  You
  can get a proc-file dump at the current state, get a list of control
  (mixer) elements, set/get the control element value, simulate the PCM
  operation, the jack plugging simulation, etc.
  
  The package is found in:
  
  - ftp://ftp.suse.com/pub/people/tiwai/misc/
  
  A git repository is available:
  
  - git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/hda-emu.git
  
  See README file in the tarball for more details about hda-emu
  program.
  
  
  hda-jack-retask
  ~~~~~~~~~~~~~~~
  hda-jack-retask is a user-friendly GUI program to manipulate the
  HD-audio pin control for jack retasking.  If you have a problem about
  the jack assignment, try this program and check whether you can get
  useful results.  Once when you figure out the proper pin assignment,
  it can be fixed either in the driver code statically or via passing a
  firmware patch file (see "Early Patching" section).
  
  The program is included in alsa-tools now:
  
  - git://git.alsa-project.org/alsa-tools.git