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From: Hans Petter Selasky <hselasky@FreeBSD.org>
Date: Thu, 19 Mar 2015 15:32:56 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r280262 - head/share/man/man4
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Author: hselasky
Date: Thu Mar 19 15:32:55 2015
New Revision: 280262
URL: https://svnweb.freebsd.org/changeset/base/280262

Log:
  Add more known bugs to the USB audio manual page.
  
  MFC after:	1 week

Modified:
  head/share/man/man4/snd_uaudio.4

Modified: head/share/man/man4/snd_uaudio.4
==============================================================================
--- head/share/man/man4/snd_uaudio.4	Thu Mar 19 14:09:27 2015	(r280261)
+++ head/share/man/man4/snd_uaudio.4	Thu Mar 19 15:32:55 2015	(r280262)
@@ -29,7 +29,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd February 24, 2011
+.Dd March 19, 2015
 .Dt SND_UAUDIO 4
 .Os
 .Sh NAME
@@ -91,12 +91,25 @@ by
 The
 .Tn PCM
 framework in
-.Fx ,
-as of this writing, does not handle device un-registrations in a properly
-abstracted manner, i.e., a detach request is refused by the
-.Tn PCM
-framework if the device is in use.
-It is necessary to allow the device un-registration to complete
-successfully, otherwise the
+.Fx
+only supports synchronous device detach.
+That means all mixer and DSP character devices belonging to a given
+USB audio device must be closed when receiving an error on a DSP read,
+a DSP write or a DSP IOCTL request.
+Else the USB audio driver will wait for this to happen, preventing
+enumeration of new devices on the parenting USB controller.
+.Pp
+Some USB audio devices might refuse to work properly unless the sample
+rate is configured the same for both recording and playback, even if
+only simplex is used. See the
+.Va dev.pcm.%d.[play|rec].vchanrate
+sysctls.
+.Pp
+The
 .Tn PCM
-layer will panic.
+framework in
+.Fx
+currently doesn't support the full set of USB audio mixer
+controls. Some mixer controls are only available as
+.Va dev.pcm.%d.mixer
+sysctls.