Re: [PATCH 12/12] arm64: dts: qcom: qcs6490-radxa-dragon-q6a: add LPASS CPU audio variant

[Val Packett <val@packett.cool>]

On 4/24/26 9:28 AM, Konrad Dybcio wrote:
> On 4/8/26 11:47 AM, Xilin Wu wrote:
>> On 4/8/2026 5:06 PM, Konrad Dybcio wrote:
>>> On 4/7/26 5:20 PM, Xilin Wu wrote:
>>>> Add a qcs6490-radxa-dragon-q6a-lpass-cpu.dts variant for debugging and
>>>> bring-up of the host-controlled LPASS audio path on the Radxa Dragon
>>>> Q6A.
>>>>
>>>> This variant enables the LPASS blocks and codec macros needed by the
>>>> lpass-cpu driver, wires WCD9380 playback/capture and DisplayPort audio
>>>> to the LPASS CDC DMA and DP interfaces, and disables remoteproc_adsp so
>>>> that the audio hardware is owned directly by Linux.
>>>>
>>>> This DTB is an optional configuration for systems booted with the kernel
>>>> running at EL2, where direct CPU access to the LPASS hardware is
>>>> available. It is useful for users who need low-latency and fully
>>>> controllable audio.
>>> I believe on Chrome platforms it was done this way because at some point
>>> it was determined that they would specifically like not to use the DSP.
>>>
>>> I think this is more of a hack than anything else.. but at the end of the
>>> commit message you mention low latency - is the impact actually measurable?
>>>
>> Some of our users also specifically prefer not to use the DSP [1] :)
>>
>> Based on their testing, the AudioReach/ADSP path imposes a minimum scheduling interval of 10 ms, which is much higher than the 0.67 ms they can get on a Raspberry Pi 5 with direct I2S/DMA.
> We passed on this feedback.
>
>> Since the lpass-cpu setup works properly, I would not consider this a hack.
> Well yeah it works, but I was really hoping it would be made
> unnecessary and available for removal sooner or later..
>
> But since there's a genuine usecase, perhaps not.

lpass-cpu is also great from a "I don't want my pure libre operating 
system to touch dirty proprietary binary blobs" perspective, but you can 
definitely argue that that's not a genuine use case :)

~val