Re: [PATCH v1 1/2] scsi: dt-bindings: ufs: Add vcc-voltage-level for UFS

Bjorn Andersson
2020-09-16T00:31:38Z

On Tue 15 Sep 03:14 CDT 2020, nguyenb@codeaurora.org wrote:

> On 2020-09-14 21:41, Bjorn Andersson wrote:
> > On Tue 01 Sep 01:00 CDT 2020, Bao D. Nguyen wrote:
> >
> > > UFS's specifications supports a range of Vcc operating
> > > voltage levels. Add documentation for the UFS's Vcc voltage
> > > levels setting.
> > >
> > > Signed-off-by: Can Guo <cang@codeaurora.org>
> > > Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
> > > Signed-off-by: Bao D. Nguyen <nguyenb@codeaurora.org>
> > > ---
> > > Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt | 2 ++
> > > 1 file changed, 2 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
> > > b/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
> > > index 415ccdd..7257b32 100644
> > > --- a/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
> > > +++ b/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
> > > @@ -23,6 +23,8 @@ Optional properties:
> > > with "phys" attribute, provides phandle
> > > to UFS PHY node
> > > - vdd-hba-supply : phandle to UFS host controller supply
> > > regulator node
> > > - vcc-supply : phandle to VCC supply regulator node
> > > +- vcc-voltage-level : specifies voltage levels for VCC supply.
> > > + Should be specified in pairs (min, max),
> > > units uV.
> >
> > What exactly are these pairs representing?
> The pair is the min and max Vcc voltage request to the PMIC chip.
> As a result, the regulator output voltage would only be in this range.
>

If you have static min/max voltage constraints for a device on a
particular board the right way to handle this is to adjust the board's
regulator-min-microvolt and regulator-max-microvolt accordingly - and
not call regulator_set_voltage() from the river at all.

In other words, you shouldn't add this new property to describe
something already described in the node vcc-supply points to.

Regards,
Bjorn

> >
> > Is this supposed to be 3 pairs of (min,max) for vcc, vcc and vccq2 to be
> > passed into a regulator_set_voltage() for each regulator?
> Yes, that's right. I should include the other power supplies in this change
> as well.
> >
> > Or are these some sort of "operating points" for the vcc-supply?
> >
> > Regards,
> > Bjorn
> >
> > > - vccq-supply : phandle to VCCQ supply regulator node
> > > - vccq2-supply : phandle to VCCQ2 supply regulator node
> > > - vcc-supply-1p8 : For embedded UFS devices, valid VCC range
> > > is 1.7-1.95V
> > > --
> > > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
> > > Forum,
> > > a Linux Foundation Collaborative Project
> > >