Re: [RFC PATCH] regulator: core: allow consumers to request tocloses step voltage

[Nishanth Menon]

On 07:45-20130620, Nishanth Menon wrote:
> On 23:38-20130619, Mark Brown wrote:
> > On Wed, Jun 19, 2013 at 02:17:54PM -0500, Nishanth Menon wrote:
> > 
> > > Account for step size accuracy when exact voltage requests are send for
> > > step based regulators.
> > 
> > If the consumer can tolerate a different voltage why not just request
> > the range that can be tolerated?  Your problem here is specifying an
> > exact voltage.
> I think you mean using regulator_get_linear_step
> 
> > 
> > > The specific example I faced was using cpufreq-cpu0 driver with voltages
> > > for OPPs for MPU rail and attempting the common definitions against voltages
> > > that are non-exact multiples of stepsize of PMIC.
> > 
> > > The alternative would be implement custom set_voltage (as againsta simpler
> > > set_voltage_sel and using linear map/list functions) for the regulator which
> > > will account for the same.
> > 
> > > Yet another alternative might be to introduce yet another custom function similar
> > > to regulator_set_voltage_tol which accounts for this. something like:
> > > regulator_set_voltage_floor(regulator, voltage, tol) or something to that effect.
> > 
> > Or as I keep telling you guys the consumer can just do that directly
> > using the existing API; the whole point in specifying the voltage as a
> > range is to allow the consumer to cope with arbatrary regulators by
> > giving a range of voltages that it can accept.
> > 
> > The API is deliberately very conservative in these matters since there
> > is a danger of physical damage if things really go wrong in some
> > applications, it makes sure that both the drivers and the system
> > integration are involved.
> I agree. The intent of this series was to start a conversation to see if
> we can make it simpler.
> 
> Searching for the users of regulator_get_linear_step in 3.10-rc6
> shows none.
> 
> For a generic driver which needs to handle platforms which
> have tolerance, they'd use regulator_set_voltage_tol. But the
> implementation would allow for uV - tol to uV + tol as range, which in
> the case I mentioned(min voltage =uV) wont work.
> 
> If the consumer wants to be aware of linear step regulator, they'd have to do:
> step_uV = regulator_get_linear_step(...);
> regulator_set_voltage(uV, uV + step_uV);
> 
> Then this wont handle tolerance. So the solution seems to be (for the
> consumer):
> step_uV = regulator_get_linear_step(...);
> ..
> if (tol)
> 	regulator_set_voltage_tol(uV, tol);
> else
> 	regulator_set_voltage(uV, uV + step_uV);
> (with the required error checks for regulator being a linear regulator
>  etc..).
> 
> At least to me, there is no sane manner to handle "tolerance" and linear step
> accuracy for a defined voltage (Should tolerance be rounded off to
> step_uV? what about the border cases etc.)
> 
> Would you agree?

Here is an RFC for the same. My hope was to see if something simpler
could be done.