ALSA: Add more documentation about HD-audio driver

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.