[alsa-devel] my udev rules are breaking my dmixer setup why?

[Takashi Iwai]

At Tue, 11 Nov 2008 12:21:30 +0100,
Jelle de Jong wrote:
> 
> Jaroslav Kysela wrote:
> > On Tue, 11 Nov 2008, Takashi Iwai wrote:
> > 
> >>> Almost all devices can be managed with udev rules, that is where the
> >>> system is designed for, there are also alsa rules in there, if they
> >>> don't work what is wrong then? is it an alsa issue, or udev, what are
> >>> the dependencies when alsa uses hardware. How are the /dev/snd/* devices
> >>> used and what is the /proc/asound/* for ?
> >> The card index mechanism in ALSA was introduced much before udev
> >> was born.  It's just a legacy mechanism, but it's hard to kill without
> >> breaking the running system, unfortunately.
> > 
> > Note that you can identify your card via the text identification (check 
> > /proc/asound/cards to get it in []). You can set this identification in 
> > the module insert time and use for example 'hw:Intel' in your apps without 
> > bothering with indexes.
> > 
> > The missing part is the modification of this text identification using
> > sysfs at runtime for udev. Some time ago, I was trying to add this setup 
> > to /sys/class/sound, but the sysfs core code was not prepared for this 
> > change. I'll try to check the situation again.
> > 
> > 					Jaroslav
> 
> I wish it was as simple as using the [identification ]. The [id..] is
> not reliable for one usb port, as you can below I just unplugged some
> usb audio devices and plugged it in again. The [id] does not match the
> same usb location port anymore, so breaking the
> user->unique-usb-port-audio-device connection.
> 
> Being able to set the id with udev would be an possible solution.

Ah, indeed.  I vaguely remember why I wrote that patch...


> cat /proc/asound/cards (first)
>  0 [Intel          ]: HDA-Intel - HDA Intel
>                       HDA Intel at 0xf7db8000 irq 16
>  1 [pcsp           ]: PC-Speaker - pcsp
>                       Internal PC-Speaker at port 0x61
>  2 [Em28xx Audio   ]: Empia Em28xx AudEm28xx Audio - Em28xx Audio
>                       Empia Em28xx Audio
>  3 [default        ]: USB-Audio - USB  AUDIO
>                       USB  AUDIO   at usb-0000:00:1d.7-4.1, full speed
>  4 [default_1      ]: USB-Audio - USB  AUDIO
>                       USB  AUDIO   at usb-0000:00:1d.7-4.2, full speed
>  5 [default_2      ]: USB-Audio - USB  AUDIO
>                       USB  AUDIO   at usb-0000:00:1d.7-4.3, full speed
>  6 [default_3      ]: USB-Audio - USB  AUDIO
>                       USB  AUDIO   at usb-0000:00:1d.7-4.4, full speed
> 
> cat /proc/asound/cards (second)
>  0 [Intel          ]: HDA-Intel - HDA Intel
>                       HDA Intel at 0xf7db8000 irq 16
>  1 [pcsp           ]: PC-Speaker - pcsp
>                       Internal PC-Speaker at port 0x61
>  3 [default        ]: USB-Audio - USB  AUDIO
>                       USB  AUDIO   at usb-0000:00:1d.7-4.3, full speed
>  4 [default_1      ]: USB-Audio - USB  AUDIO
>                       USB  AUDIO   at usb-0000:00:1d.7-4.2, full speed
>  5 [default_2      ]: USB-Audio - USB  AUDIO
>                       USB  AUDIO   at usb-0000:00:1d.7-4.4, full speed
>  6 [default_3      ]: USB-Audio - USB  AUDIO
>                       USB  AUDIO   at usb-0000:00:1d.7-4.1, full speed
> 
> Also the limitation of [0-7] devices is kind of unclear does it
> something to do with limitations of timers?

No, it's just an issue of minor device assignment.  Depending on
the kernel configuration, you'll be able to have more devices.


Takashi