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. I'm afraid I don't see any of this either documented or implemented in these patches. What is this initial detection voltage and how to you configure it? 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
