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

[nguyenb@codeaurora.org]

On 2020-09-15 06:43, Bjorn Andersson wrote:
> 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
Thank you all for your comments. The current driver hardcoding 2.7V Vcc 
min voltage
does not work for UFS3.0+ devices according to the UFS device JEDEC 
spec. However, we will
try to address it in a different way.

Regards,
Bao

> 
>> >
>> > 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
>> > >