Re: [PATCH v2 05/15] arm64: dts: freescale: imx8mn-var-som: Add support for WM8904 audio codec

[Stefano Radaelli <stefano.radaelli21@gmail.com>]

Hi Frank,

On Mon, Jul 06, 2026 at 10:00:01AM -0500, Frank Li wrote:
> On Mon, Jul 06, 2026 at 10:09:47AM +0000, sashiko-bot@kernel.org wrote:
> > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> > - [Medium] The `simple-audio-card,routing` property maps `Microphone Jack` to `IN1L` and `IN1R` but omits the connection to the `MICBIAS` supply, which will leave standard electret microphones unpowered.
> > --
> >
> > commit 78e4da0f71f2e53ae4312cbe5ceecb0f6f2345db
> > Author: Stefano Radaelli <stefano.r@variscite.com>
> >
> > arm64: dts: freescale: imx8mn-var-som: Add support for WM8904 audio codec
> >
> > This commit adds support for the WM8904 audio codec on the VAR-SOM-MX8MN board.
> > It configures the device on the I2C bus, enables the SAI peripheral, and adds a
> > simple-audio-card sound node to expose the sound card to the system.
> >
> > > diff --git a/arch/arm64/boot/dts/freescale/imx8mn-var-som.dtsi b/arch/arm64/boot/dts/freescale/imx8mn-var-som.dtsi
> > > index 09146ab763858..e2e04ad2fbb65 100644
> > > --- a/arch/arm64/boot/dts/freescale/imx8mn-var-som.dtsi
> > > +++ b/arch/arm64/boot/dts/freescale/imx8mn-var-som.dtsi
> >
> > [ ... ]
> >
> > > @@ -42,6 +50,34 @@ reg_phy_vddio: regulator-phy-vddio {
> > >  		regulator-min-microvolt = <1800000>;
> > >  		regulator-max-microvolt = <1800000>;
> > >  	};
> > > +
> > > +	sound {
> > > +		compatible = "simple-audio-card";
> > > +		simple-audio-card,bitclock-master = <&codec_dai>;
> > > +		simple-audio-card,format = "i2s";
> > > +		simple-audio-card,frame-master = <&codec_dai>;
> > > +		simple-audio-card,mclk-fs = <256>;
> > > +		simple-audio-card,name = "wm8904-audio";
> > > +		simple-audio-card,routing =
> > > +			"Headphone Jack", "HPOUTL",
> > > +			"Headphone Jack", "HPOUTR",
> > > +			"IN2L", "Line In Jack",
> > > +			"IN2R", "Line In Jack",
> > > +			"IN1L", "Microphone Jack",
> > > +			"IN1R", "Microphone Jack";
> > [Severity: Medium]
> > Will standard electret microphones remain unpowered with this routing?
> >
> > The routing maps "Microphone Jack" to "IN1L" and "IN1R", but omits a link to
> > the "MICBIAS" supply (e.g., "Microphone Jack", "MICBIAS"). Because "MICBIAS"
> > is defined as a DAPM supply widget in the codec driver, DAPM will not enable
> > it unless it has an explicit routing link connecting it to the active audio
> > path. This could leave the microphone without its required bias voltage when
> > recording.
> 
> Is this true?
> 
> Frank
> 

Thanks for pointing this out.

This audio routing is not new for this board. It follows the same WM8904
routing that we have been using on our other platforms for quite some
time, and we are not aware of any reported issues related to the
analogue microphone path.

If adding an explicit route to MICBIAS is indeed required by the
codec driver, then this would not be specific to this board but would
potentially apply to all of our WM8904-based platforms.

I'd prefer not to introduce this functional change as part of this DTS
alignment series without validating it across all affected platforms.
If needed, we can investigate the MICBIAS routing separately and
submit a dedicated fix covering all WM8904-based boards.

Thanks,
Stefano