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

[Pierre-Louis Bossart]

>>> 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.

see the example shared by Curtis

SUBSYSTEM=="pci", ATTR{vendor}=="0x8086", ATTR{device}=="0xa0c8", 
ATTR{class}=="0x040100", ATTRS{[dmi/id]board_name}=="Eldrid", 
RUN+="/sbin/modprobe snd_sof_pci tplg_path=intel/sof-tplg/pdm1"

Those 'path' parameters would have to be set prior to creating the card, 
making them writable via sysfs would not work, the firmware and topology 
are already loaded and changing the paths would have no effect.

>> 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).

you lost me with 'match the modified parameters' wording. who matches 
and who modifies those parameters?