Re: [PATCH v1 1/1] arm64: dts: imx91-var-dart-sonata: add RGB select supply for PCA6408

Frank Li
2026-03-27T18:41:44Z

On Fri, Mar 27, 2026 at 06:16:34PM +0100, Stefano Radaelli wrote:
> Hi Frank,
>
> On Fri, Mar 27, 2026 at 12:51:25PM -0400, Frank Li wrote:
> > On Fri, Mar 27, 2026 at 05:32:43PM +0100, Stefano Radaelli wrote:
> > > From: Stefano Radaelli <stefano.r@variscite.com>
> > >
> > > RGB_SEL controls the routing of some carrier board lines on the Sonata
> > > board. The two PCA6408 GPIO expanders depend on that path being enabled,
> > > so describe the selector as a fixed regulator and use it as their
> > > vcc-supply.
> >
> > Does below resolve your problem?
> > https://lore.kernel.org/imx/20260325-pinctrl-mux-v4-0-043c2c82e623@nxp.com/
> >
> > So needn't hack select as regualtor
> >
>
> Thanks for pointing me your patch, interesting improvement!
>
> Actually, in this case RGB_SEL is not meant to model a selectable mux
> on the Sonata carrier.
> On this board it must stay asserted permanently, otherwise the
> downstream path to the two PCA6408 expanders is not accessible.

Accroding to signal name, it is MUX chip select signal. Of couse it may
connect to a buffer's EN pin. I have not checked your schematic.

If it connect to MUX chip or some select signal, it should use above method,
even though it is permanently asserted when access PCA6408.

If it connect to EN pin of buffer, regualtor should be good.

Frank

>
> Modeling it as a mux might be confusing for users of the DART-MX91, as
> as it would suggest that the routing is configurable, while on this
> board it is actually fixed.

>
> Best Regards,
> Stefano