Re: Fwd: [linux-pm] Power Domain Framework

[Sundar]

On Mon, May 17, 2010 at 8:03 PM, Mark Brown
<broonie@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, May 17, 2010 at 07:03:57PM +0530, Sundar wrote:
>
> There's two problems I see.  One is expressing the operating modes in a
> way that is suitably abstract and will work for more than one chip.
Okay.

> other is that as soon as the regulator driver has to know something
> about the consumers you're running into trouble.
>
> The major goal of the regulator API is to allow us to match up consumer
> drivers with regulator drivers without having any device specific tie
> between the two.  Pushing things that need such tie in through the API
> breaks that.
>
Aren't machine constraints, setting maximum current limit based on total loads
similar to primitive tie ups between devices and regulator driver?

> Are you sure about these statements?  Bear in mind that with a regulator
> on a separate device there is no direct way for the regulator to know
> anything about what the device it is supplying is doing, and not only
> are latency requirements for mode changes are very tight but there may
> not be any software running when the mode changes which is in a position
> to relay information to the regulator.  The trend with regulators
> appears to be rather more towards removal of user visible control of the
> internal operating modes of the regulator itself with the device
> reconfiguring itself based on the ability to achieve good regulation at
> a given load point.  This gives good responsivness and efficiency over
> the full range of loads.
I am still confused about the knowledge of regulator about its consumer. How
I see is, with the added controls, it is still devoid of any
information about its
clients. All that a regulator still would know is if at all there are
any clients which
require it at full load. I think the function *set_optimal_load is
very similar to a OPP
control mechanism. Instead of summing up load currents, now there are
constraints.
Probably you may look at the patch set at the end of this mail and comment.

> have various power modes doesn't impact on the regulator except in that
> it may be able to get some information about the range of currents being
> supplied.  The converse also applies - the consumer doesn't really need
> to know anything about what the regulator is up to internally.
IMO, this leads to a more decisive control over what state the
regulator *can* be in;
without affecting any child clients.

> The big difference is that the on-SoC power domain configuration does
> frequently rely on an abstraction other than the simple voltage plus
> load one that the regulator API represents, as I said this frequently
which is what I see as that can be bridged down.

> includes a strong tie in with information about the device clocking.
> Typically changing the operating mode will change or limit the clock
> rates in use in various parts of the device.
cannot these be handled with existing/new notifiers in place?

Regards,
Sundar
P.S : Let me post out the patch set following on.
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