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

[Jaroslav Kysela]

Dne 09. 04. 21 v 9:39 Takashi Iwai napsal(a):
> On Thu, 08 Apr 2021 20:51:41 +0200,
> Pierre-Louis Bossart 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.
>>
>> 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.
> 
> Couldn't the driver probe the firmware files with some device-specific
> string suffix at first?  e.g. the driver can issue request_firmware()
> with $base_file-$dmi_board at first, then falls back to the generic
> $base_file.  A similar method was already used in Broadcom WiFi
> driver.
> 
> Also, the driver may do request_firmware() with a fixed path for the
> custom firmware at first (e.g. "intel/sof-tplg-custom"); then a system
> integrator may set up a specific configuration even that doesn't match
> with DMI or whatever identifier.

And when we have two firmware files which differs just by functionality
requested by user? Although your method will work, I won't close the
possibility to configure everything in udev rather using a hard coded fw load
scheme only.

						Jaroslav

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