via82cxxx.txt

讲述linux的初始化过程

			Via motherboard audio driver
	Copyright 1999,2000 Jeff Garzik <[e-mail]>

Driver software and documentation distributed under the GNU GENERAL
PUBLIC LICENSE (GPL) Version 2. See the "COPYING" file distributed with
this software for more info.



Introduction
------------------------------------------------------------------------
The via82cxxx audio driver found in the drivers/sound directory
of the kernel source tree is a PCI audio driver for audio chips
found on Via-based motherboards, such as the MVP4.

Currently the driver exports the following features:

	* /dev/dsp and /dev/audio support
	* 16-bit stereo PCM output channel
	* AC97 mixer

Please send bug reports to the mailing list [e-mail].
To subscribe, e-mail [e-mail] with "subscribe linux-via" in the
body of the message.


Thanks
------------------------------------------------------------------------
Via for providing e-mail support, specs, and NDA'd source code.

MandrakeSoft for providing hacking time.

AC97 mixer interface fixes and debugging by Ron Cemer <[e-mail]>



Installation
------------------------------------------------------------------------
If the driver is being statically compiled into the kernel, no
configuration should be necessary.

If the driver is being compiled as a module, generally one line must
be added to your /etc/conf.modules (or /etc/modules.conf) file:

	alias sound via82cxxx_audio



Driver notes
------------------------------------------------------------------------
Two /proc pseudo-files provide diagnostic information.  This is generally
not useful to most users.  Power users can disable VIA_PROC_FS macro in the 
driver source code, and remove the /proc support code.  In any case, once
version 2.0.0 is released, the /proc support code will be disabled by
default.  Available /proc pseudo-files:

	/proc/driver/via/0/info
	/proc/driver/via/0/ac97

This driver by default supports all PCI audio devices which report
a vendor id of 0x1106, and a device id of 0x3058.  Subsystem vendor
and device ids are not examined.

Only supports a single sound chip, as this is a motherboard chipset.
Some architecture remains for multiple cards, feel free to submit
a patch to clean some of that up.  Ideally, 

No consideration for SMP, this chipset is not known to be found on
any SMP motherboards.  However, spin_locks must be used anyway in order
to handle interrupts correctly.

GNU indent formatting options:  -kr -i8 -pcs



Tested Hardware
------------------------------------------------------------------------
The following is an _incomplete_ list of motherboards supported by this
audio driver.  If your motherboard (or notebook) is not listed here,
please e-mail the maintainer with details.

	AOpen MX59 Pro
	Compaq Presario 1247



Random Developer Notes / Comments
------------------------------------------------------------------------
Via has graciously donated e-mail support and source code to help further
the development of this driver.  Their assistance has been invaluable
in the design and coding of the next major version of this driver.

The Via audio chip apparently provides a second PCM scatter-gather
DMA channel just for FM data, but does not have a full hardware MIDI
processor.  I haven't put much thought towards a solution here, but it
might involve using SoftOSS midi wave table, or simply disabling MIDI
support altogether and using the FM PCM channel as a second (input? output?)



General To-do List (patches/suggestions welcome)
------------------------------------------------------------------------
Recording support

mmap support

Other advanced ioctls

Better docs

Code review

Native MIDI driver, as described above



Known bugs (patches/suggestions welcome)
------------------------------------------------------------------------
1) Volume too low on many systems.  Workaround:  use mixer program
such as xmixer to increase volume.

2) RealPlayer output very scratchy.  Workaround:  use esd, and
configure RealPlayer to output to esd.

3) Applications which attempt to open the sound device in read/write
mode (O_RDWR) will fail.  This is incorrect OSS behavior, but since
this driver will eventually support recording as well as playback,
we will be able to (in the future) support even broken programs which
unconditionally use O_RDWR.



Submitting a bug report
------------------------------------------------------------------------
Describe the application you were using to play/record sound, and how
to reproduce the problem.

Obtain the via-audio-diag diagnostics program from
http://gtf.org/garzik/drivers/via82cxxx/ and provide a dump of the
audio chip's registers while the problem is occurring.  Sample command line:
	./via-audio-diag -aps > diag-output.txt

Define "VIA_DEBUG" at the beginning of the driver, then capture and email
the kernel log output.  This can be viewed in the system kernel log (if
enabled), or via the 'dmesg' program.

If you wish to increase the size of the buffer displayed by 'dmesg', then
change the LOG_BUF_LEN macro at the top of linux/kernel/printk.c, recompile
your kernel, and pass the "-s <size>" option to 'dmesg'.



Change history
------------------------------------------------------------------------
Version 1.1.7:
* Fix module unload bug where mixer device left registered
  after driver exit

Version 1.1.6:
* Rewrite via_set_rate to mimic ALSA basic AC97 rate setting
* Remove much dead code
* Complete spin_lock_irqsave -> spin_lock_irq conversion in via_dsp_ioctl
* Fix build problem in via_dsp_ioctl
* Optimize included headers to eliminate headers found in linux/drivers/sound

Version 1.1.5:
* Disable some overly-verbose debugging code
* Remove unnecessary sound locks
* Fix some ioctls for better time resolution
* Begin spin_lock_irqsave -> spin_lock_irq conversion in via_dsp_ioctl

Version 1.1.4:
* Completed rewrite of driver.  Eliminated SoundBlaster compatibility
  completely, and now uses the much-faster scatter-gather DMA engine.