Re: [PATCHv9 1/3] Runtime Interpreted Power Sequences

Alex Courbot
2012-11-21T01:56:36Z

Hi Tomi,

On Tuesday 20 November 2012 22:48:18 Tomi Valkeinen wrote:
> I guess there's a reason, but the above looks a bit inconsistent. For
> gpio you define the gpio resource inside the step. For power and pwm the
> resource is defined before the steps. Why wouldn't "pwm = <&pwm 2
> 5000000>;" work in step2?

That's mostly a framework issue. Most frameworks do not export a function that
allow to dereference a phandle - they expect resources to be declared right
under the device node and accessed by name through foo_get(device, name). So
using phandles in power sequences would require to export these additional
functions and also opens the door to some inconsistencies - for instance, your
PWM phandle could be referenced a second time in the sequence with a different
period - how do you know that these are actually referring the same PWM
device?

> > +When a power sequence is run, its steps is executed one after the other
> > until +one step fails or the end of the sequence is reached.
>
> The document doesn't give any hint of what the driver should do if
> running the power sequence fails. Run the "opposite" power sequence?
> Will that work for all resources? I'm mainly thinking of a case where
> each enable of the resource should be matched by a disable, i.e. you
> can't call disable if no enable was called.

We discussed that issue already (around v5 I think) and the conclusion was
that it should be up to the driver. When we simply enable/disable resources it
is easy to revert, but in the future non-boolean properties will likely be
introduced, and these cannot easily be reverted. Moreover some drivers might
have more complex recovery needs. This deserves more discussion I think, as
I'd like to have some "generic" recovery mechanism that covers most of the
cases.

Alex.