Re: Device tree binding for DVFS table

On Wed, Jul 11, 2012 at 10:04:02PM +0200, Mike Turquette wrote:

On 20120711-15:44, Mark Brown wrote:

quoted

On Wed, Jul 11, 2012 at 09:03:41AM -0500, Rob Herring wrote:

quoted

I'd expect a single property with freq/volt pairs or 2 properties for
freq and voltage where there is a 1:1 relationship (freq N uses voltage N).

I strongly agree - the current proposal is very hard to read due to the
separation between the voltage and frequency values.  Some devices do
also need to scale multiple rails together, especially when this gets
used for I/O devices.

I'd also expect to see a range of voltages for each frequency rather
than a specific voltage; usually things are at least characterised with
a specified tolerance.

Not only should we support multiple voltage rails but also multiple
clocks.  For some devices a DVFS transition is composed of scaling
multiple clock rates together.  So some sort of clock identifier
(phandle?) is needed as well.  (forgive my ignorance on the phandle
part, as I am a DT noob)

I would say this constraint should be expressed in a seperate DT node. In
short I think we have 3 things to model:

+ frequency/voltage relationships
+ power rail constraints (eg voltage difference limit between 2 rails)
+ clock constraints (eg. clock x frequency must be a fixed ratio of clock y
  frequency)

Cheers,

Peter.