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

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Date:   Tue, 15 Sep 2020 08:43:35 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     nguyenb@...eaurora.org
Cc:     cang@...eaurora.org, asutoshd@...eaurora.org,
        martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Avri Altman <Avri.Altman@....com>,
        Vinod Koul <vkoul@...nel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/2] scsi: dt-bindings: ufs: Add vcc-voltage-level for
 UFS

On Tue 15 Sep 03:14 CDT 2020, nguyenb@...eaurora.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@...eaurora.org>
> > > Signed-off-by: Asutosh Das <asutoshd@...eaurora.org>
> > > Signed-off-by: Bao D. Nguyen <nguyenb@...eaurora.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
> > >