kern/47236: hdaudio/mixer initialization badly wrong on Thinkpad X61s

[graham.willmott%blueyonder.co.uk@localhost]

>Number:         47236
>Category:       kern
>Synopsis:       hdaudio/mixer initialization badly wrong on Thinkpad X61s
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Nov 22 17:25:00 +0000 2012
>Originator:     Graham Willmott
>Release:        6.0 Release
>Organization:
>Environment:
NetBSD  6.0 NetBSD 6.0 (GENERIC) i386
>Description:
Tried installing NetBSD 6.0 on a Lenovo Thinkpad X61s. Fairly shortly into the 
kernel startup, the machine started to emit a continuous and unbearably loud 
squealing noise. This sounds very much like badly dying fan, and even changes 
pitch and loudness when you tilt the computer, like a dying fan. But it's not a 
hardware problem.

I found that plugging something into the headphone socket makes the squeal go 
away. It seems that the default mixer configuration is routing the internal mic 
straight out to the nearby internal speaker, resulting in a very loud screech 
of audio feedback.

The machine is essentially unusable unless you realize that this is what's 
going on.

>How-To-Repeat:
Just boot the generic kernel.

>Fix:
WORKAROUND:

1) plug headphones in during installation
2) when installed and booted, issue "mixerctl -w inputs.record2.mute=on"; this 
will shut it up
3) only ever reboot when you have headphones available to plug in :)


A proper fix would require all audio inputs to be either muted or correctly 
routed when the drivers load.