Re: [PATCH 1/4] regulator: core: Support trying to get close to a certain voltage

[Doug Anderson]

Mark,

On Thu, Dec 11, 2014 at 4:24 PM, Mark Brown <broonie@xxxxxxxxxx> wrote:
> On Thu, Dec 11, 2014 at 11:55:55AM -0800, Doug Anderson wrote:
>> On Thu, Dec 11, 2014 at 9:09 AM, Mark Brown <broonie@xxxxxxxxxx> wrote:
>
>> > Please also bear in mind the need to handle shared supplies in your
>> > implementation.
>
>> I'm being dense, can you give more details?  Do you want me to grab
>> the mutex or do something smarter like track the voltage / tolerance
>> requested by multiple clients and resolve them, or ...?
>
> I mean the latter - what happens if more than one consumer is trying to
> use the regulator?  This is IIRC why _set_voltage_tol() uses the cheap
> and nasty implementation it does.

Ah, I see.  I don't think I've ever encountered a case where there
were two consumers for a regulator that actually requested voltages...

...but isn't regulator_set_voltage_tol() broken there?  If you have
two clients, A and B and a regulator that can go 1.0V to 5.0V in .05V
increments:

A requests 1.8V +/- .1V.  We get 1.8V
B requests 1.7V +/- .05V.

The above could be achievable with a voltage of 1.75V but it won't
work with the current regulator_set_voltage_tol() I think.


> There's also the potential
> performance considerations for the DVS type applications now I think
> about it.

Iterating through voltages is really that slow?  If so, perhaps we
could add some caching to keep track of what voltage we actually got
last time...  I could also add an optimization to try the exact
requested voltage right away...

-Doug
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