Re: [PATCH 6/7] ASoC: Intel: soc-acpi-intel-tgl-match: add cs42l43 and cs56l56 support

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

>>>>>> +        .name_prefix = "cs35l56-8"
>>>>>
>>>>> Can these prefixes be "AMPn" to match the CS35L41, CS35L51 and
>>>>> CS35L56-hda driver? This prefix is used to find the matching firmware
>>>>> files and our naming convention for these has been cs35lxx-xxxx-ampn
>>>>>
>>>>> Is there anything that depends on the prefixes being "cs35l56-n" ?
>>>>
>>>> IIRC this name_prefix is just used for the codec_conf and hence for
>>>> control names/UCM. At some point userspace/driver need to know if amp5
>>>> is left or right.
>>>>
>>>> We can certainly align on conventions but the values set in this ACPI
>>>> match table will not be used for firmware download - different scope.
>>>>
>>>
>>> They are used for our firmware download. Each amp can have its own
>>> unique firmware file. The ALSA prefix is used to identify which firmware
>>> file to load to which amp.
>>
>> The prefix will only be used when the card is created, specifically for
>> control names.
>> The firmware should be selected and downloaded when the device shows up
>> on the bus.
>> Card creation and device enumeration/initialization happen on different
>> timelines, if the machine driver is "blacklisted" or unbound I am not
>> sure what happens.
>>
>> There is a dependency between machine driver probe and codec firmware
>> download that I am not able to follow, can you please elaborate?
>>
> 
> The codec driver has to choose which firmware to load from under
> /lib/firmware. It does this using a combination of SSID (to identify the
> target product), the ALSA prefix string (to identify which amp) and
> in some systems a GPIO on the motherboard to select between different
> models of speaker when they have multiple suppliers. This results in a
> firmware name like:
> 
> cs35l56-<silicon rev>-dsp1-misc-<SSID>[-<SPEAKER MODEL>]-<ALSA PREFIX>
> 
> You can see this if you look in the linux-firmware repo under cirrus/
> for cs35l41 firmware files (though the ALSA PREFIX section in those
> cases is not "AMPn" because they are not SDCA parts with rotation,
> they have a fixed left/right assignment.)
> 
> We have to be careful of the length of the prefix. The 44 characters of
> an ALSA control name get eaten up very quickly when we start creating
> fully-qualified names for controls published by the firmware. So "AMPn"
> was nice because it was descriptive enough but only uses 5 characters
> of the 44.
> 
> Having said that, I've calculated that we have enough characters (just)
> to use a prefix of "cs35l56-n". If there's a reason why that is
> necessary/desirable for SOF or SoundWire then we could do that. But we'd
> intended to use "AMPn" prefixes.
> 
> We just need to decide whether to go with "AMPn". Or switch to using
> "cs35l56-n" for the ALSA prefix (the therefore the qualifier at the end
> of the firmware filename).

Yes we have similar issues with control names in topology, the limit is
hit very quickly.

I think you missed my point though that the ALSA prefix is only set when
the card is created, which can be sometime after the firmware needs to
be downloaded. I guess you could pick the firmware in the component
probe, which happens during the card creation, but that could be
sub-optimal. Given the download times you want the download to proceed
as early as possible.