On Wed, 26 Feb 2003, Ivica Bukvic wrote:
> Hi all,
>
> After several correspondence between the CCRMA's Linux audio guru
> Fernando and myself, I realized that Alsa really needs (as Fernando has
> pointed out) list of modules currently loaded that would enable users to
> simply plug in devices as needed and then have them immediately
> recognized by Alsa without having to restart the alsasound server (or
> perhaps have it restart automatically -- although now that I think of
> it, this would be a hack-like approach that would wreak havoc among the
> open apps talking to the audio resources at the time of its restart).
>
> The typical example of problems that arise due to fact that this is not
> available is with the Midisport 2x2 USB interface (something that is
> applicable to any other hot-pluggable audio/midi interface).
>
> Scenario 1:
>
> If one enables loading of the Midisport 2x2 interface at boot time, then
> the device loads before the actual soundcard (since alsasound service
> starts after the USB service -- something that is apparently not
> configurable). This results in an absent /dev/dsp (since midisport is
> the default audio device and it has no audio capabilities) and a
> hardlock if pd is spawned having Midisport being the 1st audio device
> (and possibly a plethora of other, yet-to-be-discovered side-effects).
> Having index values in modules.conf does not solve the problem, since
> USB still starts before Alsasound does, and therefore USB hw is to the
> best of my knowledge unaffected by it. The only solution is to hook-up
> your USB equipment after the alsasound service starts (this is ok, but
> not acceptable as a 100% user-friendly experience, since one that does
> not know of this issue, such as myself a week ago, ends up crashing the
> machine X times before realizing the problem, and that is if they ever
> get to realize it -- I consider myself relatively Linux/Alsa literate,
> and yet even I was feeling lost there for a while).
>
> Scenario 2:
>
> On the other hand if one blacklists loading of the snd-usb-midi at the
> moment that Midisport 2x2 is detected (at boot-time) in order to have
> Alsa configure itself properly through the modules.conf script
> afterwards, this means that if one does not plug in the Midisport 2x2
> before alsasound service starts (at boot-time), they are forced to
> restart alsasound service in order to have their USB hw functional
> (which may again wreak havoc on the open audio apps using audio
> resources and furthermore requires relatively good knowledge of the
> underlying problem as well as the concept of Linux services etc.).
>
>
> Both of the situations are apparently unacceptable from an average
> end-user standpoint since they imply that the end-user needs to know
> these quirks in order to have basic (ok, not-so-basic :-) Alsa's
> functionality.
>
> Here's the excerpt from Fernando's comments which suggest a potentially
> easy fix to the problem, something that would make Alsa a _lot_ more
> user-friendly.
>
> <quote>
>
> "The proper fix to all this problem would be to modify the alsasound
> startup script to be able to load the missing modules (ie: start a
> partially started module load). There was a thread in one of the mailing
> lists about this and to do it cleanly it would be nice to have available
> in /proc/asound the list of modules currently loaded. That is not
> available today (I think Takashi said he might add that)."
>
> <end-quote>
>
> Fernando mentions that there was already a thread on this issue and that
> Takashi generously offered to do this at some point (and I am sure that
> he's busy already as it is). However, it seems that this should be
> something that needs more urgent attention, especially now that we have
> seen a rapid increase in support of hot-pluggable audio hardware
> (usb/pcmcia, and hopefully soon the firewire stuff).
Note that the problem is already solveable with a nice way. The SuSE uses
this hotplug script:
-------------------------
#!/bin/bash
#
# /etc/hotplug/usb/alsasound
#
# Sets up newly plugged in USB audio/MIDI devices.
#
if [ "$INTERFACE" != "" ]; then
IFS=/
set $INTERFACE ''
usb_bInterfaceClass=$1
usb_bInterfaceSubClass=$2
usb_bInterfaceProtocol=$3
IFS="$DEFAULT_IFS"
fi
function add_alsa () {
# check alsa is already running
if [ ! -d /proc/asound ]; then
# start alsasound script, so that static devices are properly loaded
echo "Starting ALSA..."
/etc/init.d/alsasound start >/dev/null 2>&1
fi
/sbin/modprobe snd-usb-audio
if [ "$usb_bInterfaceSubClass" != "0x01" ]; then
/sbin/modprobe snd-usb-midi
fi
}
function remove_alsa () {
/sbin/modprobe -r snd-usb-midi
/sbin/modprobe -r snd-usb-audio
}
case "$ACTION" in
add)
add_alsa
;;
remove)
remove_alsa
;;
esac
-----------------------
So, if no static ALSA drivers are loaded, load them before usb module is
inserted. Nice way to solve all your problems.
Jaroslav
-----
Jaroslav Kysela <[EMAIL PROTECTED]>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs
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