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

[Xilin Wu]

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.

Since the lpass-cpu setup works properly, I would not consider this a hack.

[1] 
https://forum.radxa.com/t/dragon-q6a-lpaif-mi2s-registers-locked-by-qualcomm-trustzone-no-direct-low-latency-audio-access-possible/30592

> Konrad


--
Best regards,
Xilin Wu <sophon@xxxxxxxxx>