Re: [PATCH] ALSA: core - add more card sysfs entries

[Jaroslav Kysela <perex@perex.cz>]

Dne 08. 04. 21 v 17:32 Pierre-Louis Bossart napsal(a):
> 
> 
> On 4/8/21 10:01 AM, Jaroslav Kysela wrote:
>> When we have a common standard layer for the plug-and-play handling (udev), we
>> should concentrate to allow changing / refining of this information there.
>> Those strings are not used for anything else than the user space. So from my
>> view, there's no reason to create another mechanism to handle the overrides.
>> It should be a safe, fast, flexible and_optional_  solution. The udev can
>> alter the sysfs attributes directly without any hassle with the file
>> modifications or looking for another way to pass / store this information
>> somewhere.
> 
> There's one part where I am lost.
> 
> The initial idea of udev what to modify kernel parameters to pick a 
> different path for firmware/topology before probing the PCI driver. At 

This may be a problematic point. The kernel cmdline cannot be modified from
udev (as far as I know). The module parameters can be set using modprobe's
config files or when loaded with sysfs attributes (/sys/module/*/parameters).
Eventually, you can call the modprobe command with custom module parameters
when the appropriate MODALIAS is probed.

Perhaps, I'm missing something here, too. Some example udev rules may help.

> that point there is no card and no sysfs attributes just yet, they will 
> be added at a later point during the probe itself.
> 
> So are we talking about a second set of rules that would be applied when 
> the card is created?

Yes, I'm talking about rules which depends on the sound driver specific sysfs
attributes (you can match the modified /sys/module/*/parameters here).

						Jaroslav

-- 
Jaroslav Kysela <perex@perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.