RFC: Regulator Framework Voltage Setting

RFC: Regulator Framework Voltage Setting

[Linus WALLEIJ]

Hello,

we have a question regarding the regulator_set_voltage function in the 
regulator framework (drivers/regulator/core.c). The current 
implementation checks the input min and max arguments against the 
constraints and then calls the driver set_voltage operation directly 
without checking the other consumer requests.

In our view it should respect all consumer voltage settings. Then, the 
implementation would (roughly) be to iterate through all consumers and 
make sure all of their latest requests are satisfied.

Our questions:
- Is this the correct interpretation of the current functionality?
- Is the proposed behaviour what you would expect?
- Any other problems to consider?

Below we have given an example to clarify.

Best regards,

Bengt JONSSON
Sundar R IYER
Linus WALLEIJ



Here is an example with three users (consumers) connected to the same 
regulator_dev:

rdev ------ xreg (User X)
        |--- yreg (User Y)
        |--- zreg (User Z)

The users call the regulator framework like this:

1. User X calls regulator_set_voltage(xreg, 2000000, 3000000)
2. User Y calls regulator_set_voltage(yreg, 2100000, 3100000)
3. User Z calls regulator_set_voltage(zreg, 1900000, 2900000)
4. User Y calls regulator_set_voltage(yreg, 1900000, 3100000)
5. User Z calls regulator_set_voltage(zreg, 1900000, 3100000)
6. User X calls regulator_set_voltage(xreg, 4000000, 5000000). Here the 
call should fail.

Assuming there are no constraints, with current implementation, the 
requests would be sent unchanged to the driver. What we would expect 
from the regulator framework is this:

1. The framework calls rdev->desc->ops->set_voltage(rdev, 2000000, 3000000)
2. The framework calls rdev->desc->ops->set_voltage(rdev, 2100000, 3000000)
3. The framework calls rdev->desc->ops->set_voltage(rdev, 2100000, 2900000)
4. The framework calls rdev->desc->ops->set_voltage(rdev, 2000000, 2900000)
5. The framework calls rdev->desc->ops->set_voltage(rdev, 2000000, 3000000)
6. Failed because the ranges do not overlap.

Re: RFC: Regulator Framework Voltage Setting

[Mark Brown]

On Wed, Jun 02, 2010 at 11:18:00AM +0200, Linus WALLEIJ wrote:

> Our questions:
> - Is this the correct interpretation of the current functionality?
> - Is the proposed behaviour what you would expect?
> - Any other problems to consider?

The current expectation is that a consumer that really needs a voltage
setting will have exclusive use of the regulator and won't share it with
other consumers.  There was some support for combining constraints from
multiple consumers originally but it got removed due to requests from
David Brownell (there's not actually much demand for this feature
anyway, finding devices which support but do not required DVS is
actually quite hard and generally the power requirments for shared rails
get fixed at hardware build tiem).