ALSA: Add more documentation about HD-audio driver

The file can be converted to PDF via asciidoc.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

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+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 rest is the driver implementation.  This
+document explains the 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.  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 some cases, there can be
+multiple audio codecs, e.g. for analog and digital outputs, but the
+driver might not work properly.
+
+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 reads from the io-mapped
+position-buffer, and falls back to LPIB if it appears unupdated.
+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.  0 is the default
+value, the automatic check.  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
+chip, 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 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 destruct the further communication
+with the codec chips.  The symptom appears usually as the error
+message 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
+corresponding 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.
+
+
+Interrupt Handling
+~~~~~~~~~~~~~~~~~~
+In rare but some cases, the interrupt isn't properly handled as
+default.  You would notice this by the DMA transfer error reported by
+ALSA PCM core, for example.  Using MSI might help in such a case.
+Pass `enable_msi=1` option for enabling MSI.
+
+
+HD-AUDIO CODEC
+--------------
+
+Model Option
+~~~~~~~~~~~~
+The most common problems with 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: Unknown model for ALC880, trying auto-probe from BIOS...
+------------------------------------------------------------------------
+Even if you 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 list.  But, this doesn't mean that the driver
+is broken.  Many codec-driver provides the automatic configuration
+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 is provided basically to override such a situation.
+When the matching preset model is found in the list, the driver
+assumes the static configuration of that preset and builds the mixer
+and PCM based on the static information.  Thus, if you have a newer
+machine with a slightly different PCI 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 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/ALSA-Configuration.txt file.
+In 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
+HD-audio hardware is to check HD-audio codec and several different
+`model` option values.  If you have a luck, some of them might suit
+with your device well.
+
+Some codecs such as ALC880 have a special model option `model=test`.
+This configures the driver to provide as many mixer controls as
+possible for every single pin feature except for the unsolicited
+events (and maybe some other specials).  Adjust each mixer element and
+try the I/O in the way of trial-and-error until figuring out the whole
+I/O pin mappings.
+
+Note that `model=generic` has a special meaning.  It means to use the
+generic parser regardless of the codec.  Usually the codec-specific
+parser is much better than the generic parser (as now).  Thus this
+option is more about the debugging purpose.
+
+
+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 amplifier.  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.  In addition, there
+are 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) can 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 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.  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.
+
+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 touch guy
+to fight again the 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".
+
+
+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 choose the option for other vendors.  If you are unsure, just
+choose 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
+hda-verb program.  For example, `hwC0D2` will be created for the card
+0 codec slot #2.  For debug tools such as hda-verb and hda-analyzer,
+the hwdep device has to be enabled.  Thus, 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 tree numbers, nid, verb and parameter.
+hints::
+  Shows hint strings for codec parsers for any use.  Right now it's
+  not used.
+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.
+
+
+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/modules/snd_hda_intel/parameters/power_save to
+check the current value.  If it's non-zero, the feature is turned on.
+
+
+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::
+  http://bugme.linux-foundation.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.
+
+
+hda-verb
+~~~~~~~~
+hda-verb is a tiny program that allows you to access the HD-audio
+codec directly.  It executes a HD-audio codec verb directly.
+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 found in the ftp directory:
+
+- ftp://ftp.kernel.org/pub/linux/kernel/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 a 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 is a part of alsa.git repository in
+alsa-project.org:
+
+- http://git.alsa-project.org/?p=alsa.git;a=tree;f=hda-analyzer
+
+
+hda-emu
+~~~~~~~
+hda-emu is a 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.kernel.org/pub/linux/kernel/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.