arm64: dts: imx8mn-var-som-symphony: add vcc supply for PCA9534

From: Hugo Villeneuve <hvilleneuve@dimonoff.com>

The following warning is shown when probing device:

    pca953x 1-0020: supply vcc not found, using dummy regulator

Add fixed 3.3v regulator as vcc supply to silence the warning.

Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
---
 arch/arm64/boot/dts/freescale/imx8mn-var-som-symphony.dts | 1 +
 1 file changed, 1 insertion(+)


base-commit: d2f51b3516dade79269ff45eae2a7668ae711b25

On 06/11/2023 19:57, Hugo Villeneuve wrote:
> From: Hugo Villeneuve <hvilleneuve@dimonoff.com>
> 
> The following warning is shown when probing device:
> 
>     pca953x 1-0020: supply vcc not found, using dummy regulator
> 
> Add fixed 3.3v regulator as vcc supply to silence the warning.
> 

This is not really a warning. It's perfectly fine to use dummy
regulator. Adding such fixed supply has sense in following cases:
1. Bindings require the supply,
2. This is in fact exactly that supply (verified on schematics).

Best regards,
Krzysztof

On Mon, 6 Nov 2023 21:39:42 +0100
Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> wrote:

> On 06/11/2023 19:57, Hugo Villeneuve wrote:
> > From: Hugo Villeneuve <hvilleneuve@dimonoff.com>
> > 
> > The following warning is shown when probing device:
> > 
> >     pca953x 1-0020: supply vcc not found, using dummy regulator
> > 
> > Add fixed 3.3v regulator as vcc supply to silence the warning.
> > 
> 
> This is not really a warning. It's perfectly fine to use dummy
> regulator. Adding such fixed supply has sense in following cases:
> 1. Bindings require the supply,
> 2. This is in fact exactly that supply (verified on schematics).
> 
> Best regards,
> Krzysztof

Hi Krzysztof,
this is case #2, but looking more closely at the carrier board
(symphony) schematics, it is not exactly the "reg_3v3_fixed" supply I
mentioned in the patch, as "reg_3v3_fixed" is located on the SOM and
only powers SOM components.

However, "reg_3v3_fixed", which is an always-on regulator (no software
enable control), is used as the enable input to a mosfet switch (Q2) on
the carrier board to generate the 3.3V (label BASE_PER_3V3 on the
schematics) used by all peripherals on that carrier board.

I guess I could then define a new "always-on" regulator labeled as,
for example, base_per_3v3, and then assign the pca953x vcc-supply
property to it?

Hugo.

On Tue, 7 Nov 2023 08:14:03 +0100
Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> wrote:

> On 06/11/2023 22:36, Hugo Villeneuve wrote:
> > On Mon, 6 Nov 2023 21:39:42 +0100
> > Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> wrote:
> > 
> >> On 06/11/2023 19:57, Hugo Villeneuve wrote:
> >>> From: Hugo Villeneuve <hvilleneuve@dimonoff.com>
> >>>
> >>> The following warning is shown when probing device:
> >>>
> >>>     pca953x 1-0020: supply vcc not found, using dummy regulator
> >>>
> >>> Add fixed 3.3v regulator as vcc supply to silence the warning.
> >>>
> >>
> >> This is not really a warning. It's perfectly fine to use dummy
> >> regulator. Adding such fixed supply has sense in following cases:
> >> 1. Bindings require the supply,
> >> 2. This is in fact exactly that supply (verified on schematics).
> >>
> >> Best regards,
> >> Krzysztof
> > 
> > Hi Krzysztof,
> > this is case #2, but looking more closely at the carrier board
> > (symphony) schematics, it is not exactly the "reg_3v3_fixed" supply I
> > mentioned in the patch, as "reg_3v3_fixed" is located on the SOM and
> > only powers SOM components.
> > 
> > However, "reg_3v3_fixed", which is an always-on regulator (no software
> > enable control), is used as the enable input to a mosfet switch (Q2) on
> > the carrier board to generate the 3.3V (label BASE_PER_3V3 on the
> > schematics) used by all peripherals on that carrier board.
> > 
> > I guess I could then define a new "always-on" regulator labeled as,
> > for example, base_per_3v3, and then assign the pca953x vcc-supply
> > property to it?
> 
> I guess this could be the same supply, even if this is not 100% true.
> However it would be good if you put above explanation in the commit msg.

Hi,
I prefer to add a new supply, and with a proper label it will be more
self-documenting, and I will still add part of this explanation to the
updated commit message.

Thank you,
Hugo.