Re: [PATCH v2 3/3] arm64: dts: qcom: Fix pm4125 vbus regulator compatible and constraints

[Dmitry Baryshkov]

On Thu, Jul 02, 2026 at 06:13:31PM +0530, Rakesh Kota wrote:
> On Thu, Jul 02, 2026 at 02:07:12PM +0200, Konrad Dybcio wrote:
> > On 7/2/26 9:33 AM, Rakesh Kota wrote:
> > > On Wed, Jul 01, 2026 at 01:26:11PM +0200, Konrad Dybcio wrote:
> > >> On 7/1/26 12:28 PM, Rakesh Kota wrote:
> > >>> Remove pm8150b fallback compatible from pm4125_vbus and fix regulator
> > >>> constraints in qrb2210 DTS files to use microvolt instead of
> > >>> microamp.
> > >>>
> > >>> Signed-off-by: Rakesh Kota <rakesh.kota@xxxxxxxxxxxxxxxx>
> > >>> ---
> > >>>  arch/arm64/boot/dts/qcom/pm4125.dtsi               | 2 +-
> > >>>  arch/arm64/boot/dts/qcom/qrb2210-arduino-imola.dts | 4 ++--
> > >>>  arch/arm64/boot/dts/qcom/qrb2210-rb1.dts           | 4 ++--
> > >>>  3 files changed, 5 insertions(+), 5 deletions(-)
> > >>>
> > >>> diff --git a/arch/arm64/boot/dts/qcom/pm4125.dtsi b/arch/arm64/boot/dts/qcom/pm4125.dtsi
> > >>> index 542e8fe030da40dfefc7b744dcc30133fdb35e74..3dc8d667d091ceb4267081d32b7aae983fc25071 100644
> > >>> --- a/arch/arm64/boot/dts/qcom/pm4125.dtsi
> > >>> +++ b/arch/arm64/boot/dts/qcom/pm4125.dtsi
> > >>> @@ -37,7 +37,7 @@ pm4125_resin: resin {
> > >>>  		};
> > >>>  
> > >>>  		pm4125_vbus: usb-vbus-regulator@1100 {
> > >>> -			compatible = "qcom,pm4125-vbus-reg", "qcom,pm8150b-vbus-reg";
> > >>> +			compatible = "qcom,pm4125-vbus-reg";
> > >>>  			reg = <0x1100>;
> > >>>  			status = "disabled";
> > >>>  		};
> > >>> diff --git a/arch/arm64/boot/dts/qcom/qrb2210-arduino-imola.dts b/arch/arm64/boot/dts/qcom/qrb2210-arduino-imola.dts
> > >>> index bf088fa9807f040f0c8f405f9111b01790b09377..2b50f3f577577d30a87fcb6466c7d7690270aaa3 100644
> > >>> --- a/arch/arm64/boot/dts/qcom/qrb2210-arduino-imola.dts
> > >>> +++ b/arch/arm64/boot/dts/qcom/qrb2210-arduino-imola.dts
> > >>> @@ -235,8 +235,8 @@ &mdss_dsi0_phy {
> > >>>  };
> > >>>  
> > >>>  &pm4125_vbus {
> > >>> -	regulator-min-microamp = <500000>;
> > >>> -	regulator-max-microamp = <500000>;
> > >>> +	regulator-min-microvolt = <4250000>;
> > >>> +	regulator-max-microvolt = <5000000>;
> > >>
> > >> Perhaps that's a stupid question, but is there any good reason to
> > >> not just keep it at 5V if enabled?
> > >>
> > > We could hardcode 5V, but keeping the range allows clients to select a
> > > lower voltage if needed. The driver supports voltage selection per use
> > > case, so hardcoding 5V would restrict that flexibility.
> > 
> > I'm trying to understand if this would ever happen in practice
> >
> Fair point.The dependent client here is the one connecting the USB
> device to the Host. We don't have a concrete example today, but the
> voltage range is kept flexible to avoid restricting future use cases.
> That said, if 5V is the agreed practical default, we're open to
> hardcoding it for simplicity.

Moreover, I think current configuration can end up with the regulator
being set to 4.25V and thus undervolting connected devices.

-- 
With best wishes
Dmitry