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? > 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. Rob
