linux-kernel - Re: [PATCH 1/2] ASoC: q6afe-dai: add dummy register read function

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Date:   Tue, 11 Aug 2020 13:04:09 +0200
From:   Stephan Gerhold <stephan@...hold.net>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:     broonie@...nel.org, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, lgirdwood@...il.com, tiwai@...e.com,
        john.stultz@...aro.org
Subject: Re: [PATCH 1/2] ASoC: q6afe-dai: add dummy register read function

On Tue, Aug 11, 2020 at 11:25:51AM +0100, Srinivas Kandagatla wrote:
> Most of the DAPM widgets for DSP ASoC components reuse reg field
> of the widgets for its internal calculations, however these are not
> real registers. So read/writes to these numbers are not really
> valid. However ASoC core will read these registers to get default
> state during startup.
> 

Actually q6afe-dai does not seem to make use of the register number.
The DAPM widgets all look like

  SND_SOC_DAPM_AIF_IN("HDMI_RX",  NULL,   0,    0,     0,      0),
                  /* (wname,    stname, wchan, wreg, wshift, winvert)

Wouldn't it be better to replace wreg = 0 with SND_SOC_NOPM in this case
so the read/write won't happen at all?

q6routing on the other hand does make use of wreg, so this would not
work there...

Also: If I remember correctly the ASoC core will also attempt to write
to these "registers" when starting to play some audio, so you might also
need to implement component->write().

Stephan