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

[nguyenb]

On 2020-09-21 17:36, Bjorn Andersson wrote:
> On Mon 21 Sep 19:22 CDT 2020, nguyenb@xxxxxxxxxxxxxx wrote:
>
> > On 2020-09-18 12:01, Rob Herring wrote:
> > > On Tue, Sep 15, 2020 at 2:10 AM <nguyenb@xxxxxxxxxxxxxx> wrote:
> > > >
> > > > On 2020-09-14 11:35, Rob Herring wrote:
> > > > > On Mon, Aug 31, 2020 at 11:00:47PM -0700, 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@xxxxxxxxxxxxxx>
> > > > >> Signed-off-by: Asutosh Das <asutoshd@xxxxxxxxxxxxxx>
> > > > >> Signed-off-by: Bao D. Nguyen <nguyenb@xxxxxxxxxxxxxx>
> > > > >> ---
> > > > >>  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.
> > > > >
> > > > > The expectation is the regulator pointed to by 'vcc-supply' has the
> > > > > voltage constraints. Those constraints are supposed to be the board
> > > > > constraints, not the regulator operating design constraints. If that
> > > > > doesn't work for your case, then it should be addressed in a common way
> > > > > for the regulator binding.
> > > > The UFS regulator has a min_uV and max_uV limits. Currently, the min
> > > > and
> > > > max are hardcoded
> > > > to UFS2.1 Spec allowed values of 2.7V and 3.6V respectively.
> > > > With this change, I am trying to fix a couple issues:
> > > > 1. The 2.7V min value only applies to UFS2.1 devices. with UFS3.0+
> > > > devices, the VCC min should be 2.4V.
> > > > Hardcoding the min_uV to 2.7V does not work for UFS3.0+ devices.
> > >
> > > Don't you know the device version attached and can adjust the voltage
> > > based on that? Or you have to set the voltage first?
> > Yes it is one of the solutions. Once detect the UFS device is version 
> > 3.0+,
> > you can lower
> > the voltage to 2.5V from the hardcoded value used by the driver. 
> > However, to
> > change the
> > Vcc voltage, the host needs to follow a sequence to ensure safe 
> > operations
> > after Vcc change
> > (device has to be in sleep mode, Vcc needs to go down to 0 then up to 
> > 2.5V.)
> > Also same sequence is repeated for every host initialization which is
> > inconvenient.
>
> It sounds like you're suggesting that we detect the UFS device using
> some voltage, then depending on version we might lower it to 2.5V.
Yes, that is one possible solution.

> I'm afraid I don't see any of this either documented or implemented in
> these patches.
I was responding to a comment about detecting the device version and 
change the voltage
based on the detection. It is not implemented in this patch. Maybe I 
should stop
discussing another possible solution, even though related to the topic, 
it is not
implemented in this patch.

> What is this initial detection voltage and how to you configure it?
The initial voltage would be 2.9V and is lowered to 2.5V if UFS3.0+ 
device is detected.
We would call the regulator_set_voltage() to set to a specific voltage 
level.

Regards,
Bao

> Regards,
> Bjorn
>
> > >
> > > > 2. Allow users to select a different Vcc voltage within the allowed
> > > > range.
> > > > Using the min value, the UFS device is operating at marginal Vcc
> > > > voltage.
> > > > In addition the PMIC and the board designs may add some variables
> > > > especially at extreme
> > > > temperatures. We observe stability issues when using the min Vcc
> > > > voltage.
> > >
> > > Again, we have standard regulator properties for this already that you
> > > can tune per board.
> > Thank you for the suggestion.
> >
> > >
> > > Rob