Re: Hotplug loads USB audio before local audio

[Christian Zoz <zoz@suse.de>]

On Thu, May 01, Pedro Lopez-Cabanillas wrote:
> On Thursday 01 May 2003 17:32, Joshua Pollak wrote:
> > Just to clarify, this problem is not particular to ALSA. I don't believe
> > RedHat 9.0 uses ALSA, I think the driver that is being loaded is the stock
> > Linux kernel one.

Yes, then modify the scripts accordingly.

> Yes, 'audio' is the OSS module for USB audio devices. OTOH, i think that your 
> problem is not particular to audio, OSS or ALSA. The problem is that you have 
> two devices of the same class, one of them supported by hotplug (or both).
> 
> For instance: if you get some internal PCI TV card using a V4L driver (as 
> bt878), and you have also an USB webcam... How can you know which is your 
> webcam /dev/video0 or /dev/video1 ? if you boot with your USB cam plugged, 
> then it is /dev/video0, but if you boot with it unplugged the node  
> /dev/video0 is your TV card, and /dev/video1 will be the webcam if you plug  
> it later. Same for printers, scanners, disks (i guess).
> 
> If you have several USB devices of the same class, you can also go into 
> troubles with your apps configured to use one device or another, by his 
> device node in /dev directory. ALSA driver snd-usb-audio has some support to 
> solve this issue, with two params to specify the device order by manufacturer 
> and model ids, but i don't know about other drivers.
> 
> Of course, you can avoid to use hotplug to load your device driver  
> (/etc/hotplug/blacklist) or renounce to use it (alias off in modules.conf). 
> The SuSE approach gives you some hotplug support, loading the drivers with 
> the classic ALSA startup script. The problem is that you need to maintain the 
> alsa.usermap file by hand as the set of devices supported by the 

Yes that's the problem. It's a kind of 'works for most users'
solution.

> snd-usb-audio driver grows (and it grows very quickly!).  Planet CCRMA 
> (stanford.edu) has a set of RPM packages for multimedia Red Hat users, using 
> /etc/hotplug/blacklist for audio, too.
> 
> David: I think that some kind of general solution for this problem should be  
> included in hotplug (if there is one).

For 2.4 kernel:
It would be best, if all services that initialize builtin hardware,
would run before USB, PCMCIA, Firewire is started. Then you always get
the same device names for this builtin hardware.
In SuSE Linux we start e.g. network before hotplug and pcmcia. But
e.g. alsa reads files from /usr/..., which may be mounted via network.
And network may be provided by pcmcia/hotplug (But this is a rare
case). So alsa starts later and therefore needs the blacklist solution.

For 2.6 this problem will hopefully solved with persistent interface
names.

-- 

ciao, christian

  --------------------------------------------------------------------
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    ist Linux geradezu eine leuchtende Perle der Datensicherheit.
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