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

[Richard Fitzgerald <rf@opensource.cirrus.com>]

On 29/11/23 16:39, Pierre-Louis Bossart wrote:
> 
>>>>>>> +        .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.

We kick off a background task from our component_probe() to do the
firmware download. We need the ALSA prefix, and also the wm_adsp library
that actually handles the DSP is ASoC code so it needs a probed
component. Doing it in a background work means it doesn't block probe().
And the download to multiple amps can proceed in parallel - obviously
that's constrained by bus bandwidth but we are seeing that they
interleave.