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

[Jaroslav Kysela]

Dne 08. 04. 21 v 21:41 Pierre-Louis Bossart napsal(a):
> 
> 
> 
>>>> 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?
>>
>> You can probably add something like this to the sound-card.rules:
>>
>> SUBSYSTEMS=="pci",ATTR{device/driver/module}=="snd_soc_sof_sdw",
>>    ATTR{device/driver/module/../snd_sof_pci/parameters/tplg_path}=="intel/sof-tplg/pdm1",
>>    DO_SOMETHING_HERE
>>
>> DO_SOMETHING_HERE may be ATTR{longname}="My Long Name" for example when my change is accepted.
> 
> Humm, not sure this can work due to dependencies.
> 
> The machine device is neither an ACPI nor PCI one. It's a platform device.
> 
> When the PCI device is detected, the PCI core will call the SOF driver 
> probe, which will first try and boot the firmware, and then create the 
> platform device. That results in the probe of the machine driver which 
> creates the card, but that happens *after* booting the firmware.
> 
> the DSP firmware is setup starting here:
> 
> https://elixir.bootlin.com/linux/latest/source/sound/soc/sof/core.c#L138
> 
> and the machine device is created almost last, after registering the 
> ASoC components.
> 
> https://elixir.bootlin.com/linux/latest/source/sound/soc/sof/core.c#L234
> 
> when the card is created, it's too late to change the firmware path or 
> any firmware-related parameters.

I just tried to describe the possible 2nd stage - modify the sysfs attributes
when the card with the modified firmware is created (all modules are loaded
and initialized). The 1st stage like from Curtis must be retained. It ensures
to load the right fw.

SYSTEMS=="pci" checks also parents and card0 links to pci device: card0 ->
../../devices/pci0000:00/0000:00:1f.3/sof_sdw/sound/card0 . You can modify
this matching anyway - the goal is to run commands for the specific driver and
module parameters when the card is loaded (avoid to change the card attributes
for other hw).

I'm not an udev expert, so there may be a bug in my suggestion. I also think
that the filter may be specified more elegantly (probably using the DRIVER
match or so).

					Jaroslav

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