Specifying the order of sound devices

[Scott James Remnant]

On Mon, 2006-04-10 at 17:00 +0100, Matthew Garrett wrote:

> On Mon, Apr 10, 2006 at 04:56:29PM +0100, Scott James Remnant wrote:
> 
> > Where both are valid choices, a choice should be made and only one
> > loaded;  if a card is supported by prism54 we should make sure
> > prism54softmac itself isn't an option.
> 
> How do you define "Not an option"? The PCI IDs are identical, and it's a 
> valid use case to want to run the softmac driver on a fullmac card.
> 
Simple; we blacklist one of the drivers.  I've said before that I have
no problem adding a "conditional blacklist" feature; where only one of
two "possible" drivers are selected.

In /etc/modprobe.d/blacklist we'd put something like:

	blacklist-if prism54 prism54softmac

Which says to blacklist prism54softmac if prism54 is *also* an option
for that card.


This isn't a complete fix though, take the following situation.

A built-in piece of hardware can be driven by driver FOO.
An additional built-in piece of hardware can be driven by driver BAR.

We load both FOO and BAR, and each only drives the appropriate card.

Now the user plugs in a removable device that's drivable by both FOO and
BAR; in this case the decision about which driver to use has to take
place in the kernel.  Module load order hasn't come into it.


There are *lots* of example situations like this; it's not tenable
waving them away with "not 95% of the time" because, frankly, your
examples are also "not 95% of the time";  99% of the time it doesn't
matter what order we load modules in.

99% of the time, we can just blacklist one of the modules.  Just like we
do for ALSA/OSS today.

It's the 1% I'm interested in, and here be lots and lots of potential
problems and I think we are much better off thinking about those because
the fixes for those also solve what the "quick fixes" solve too.

Scott
-- 
Scott James Remnant
scott at ubuntu.com
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