Re: [PATCH 1/2] regulator: DT: Add support to scale ramp delay based on platform behavior

[Laxman Dewangan]

On Saturday 19 March 2016 10:01 AM, Bjorn Andersson wrote:
> On Tue, Mar 15, 2016 at 6:41 AM, Laxman Dewangan <ldewangan@xxxxxxxxxx> wrote:
> > On Wednesday 02 March 2016 10:05 AM, Mark Brown wrote:
> > > * PGP Signed by an unknown key
> > >
> > > On Wed, Mar 02, 2016 at 09:05:26AM +0530, Laxman Dewangan wrote:
> > > > On Wednesday 02 March 2016 09:08 AM, Mark Brown wrote:
> > > > > You're not trying to scale the value here, you're trying to replace the
> > > > > value because the PMIC is incapable of delivering the advertised ramp
> > > > > rate.  Trying to express this as a multiple of the advertised ramp rate
> > > > > is just adding complexity.
> > > > So should we provide absolute ramp value here for platform specific?
> > > Yes, otherwise if the PMIC vendor respecifies their ramp rates to
> > > reflect reality and the driver is updated then your DT will be broken.
> > >
> > > > Or any other suggestion to handle this situation as this is very common
> > > > and
> > > > almost all our boards have this slowness on ramp.
> > > Perhaps time to have a chat with your PMIC vendors...
> > I had discussion with our HW team to get more information about this
> > variation.
> > They said that Maxim advertise the ramp time with given condition in
> > interface i.e. capacitance etc which is very generic.
> > We did the experiment with Maxim recommendation about the rail and its
> > capacitance (2.2uF) and found that measured value is same as what they
> > advertise in datasheet.
> >
> > When chip team use this PMIC with Tegra hardware specs and did the circuit
> > simulation to ensures how our boards should be designed for signal integrity
> > they suggested that the rail capacitance should be more than what Maxim
> > recommending in general to work with our silicon. So here condition get
> > changed and hence the effective ramp time.
> >
> > So here we will need two parameters:
> > advertised-ramp-delay for PMIC configurations and
> > ramp-delay which is measured one.
> >
> > Most of time, advertised-ramp-delay is same as ramp-delay and hence one
> > value from DT will be sufficient.
> > If there is difference then both value can be provided and
> > advertised-ramp-delay  will be used for PMIC configuration and rest of
> > calculation about delay will be from ramp-delay.
> Generally the device driver should describe the PMIC and the device
> tree should describe the board. So the Maxim's numbers should (if
> specified at all) go into the driver and the measures/calculated
> characteristics for your board should be specified in the dt.
>
> The ramp properties in the generic regulator binding is used to inform
> the OS about the board's ramp properties.
>
>
> If I understand you correctly the Maxim PMIC can be configured to
> drive the change at different speed, this should be configured through
> a Maxim specific property. It should not reuse the generic properties
> for ramp delays.

Ramp delay configurations are seen on other vendor's PMIC devices also.
Therefore, I like o me generic property rather than specific to Maxim. 
Parsing can be done in the core framework and applied during setting 
machine constraints.