[PATCH v14 03/10] qcom: spm: Add Subsystem Power Manager driver

Arnd Bergmann
2014-12-16T19:44:17Z

On Tuesday 16 December 2014 11:18:18 Stephen Boyd wrote:
> On 12/16/2014 06:38 AM, Arnd Bergmann wrote:
> > On Tuesday 16 December 2014 15:12:22 Daniel Lezcano wrote:
> >> At the beginning, all that become from not including mach files from the
> >> drivers directory which make sense.
> >>
> >> Perhaps it is time to write a similar mechanism for the cpuidle drivers
> >> where we can still separate the low level PM code from the generic
> >> cpuidle code.
> > That way you basically duplicate the same thing we already have, which
> > isn't much better.
> >
> > In the example of drivers/soc/qcom/spm.c, just call cpuidle_register
> > from the spm_dev_probe() function and be done with it. You already
> > have a device that is responsible for handling this, don't try to
> > construct more than you already need.
> >
> > I would assume that the same can be done for most other platforms.
> >
> > There are probably cases where the same piece of hardware is responsible
> > for both cpuidle and cpufreq, but what that means is really that you
> > should have a single driver for it that does both things. Same for
> > SMP support: if you have one register block that does both the SMP
> > bringup and the cpuidle stuff, then have *one* driver for this block
> > that does it all. There are currently a few dependencies that require
> > doing SMP bringup early during boot, but we decided years ago that those
> > are all artificial dependencies and we should be able to boot secondary
> > CPUs much later than we currently do.
> >
>
> +1. The SPM harware is used for hotplug, suspend, cpuidle, as well as
> provides a regulator for a CPU, so all these things should be done in a
> single driver. Booting secondary CPUs early is not hard here either if
> we move the smp ops into the same driver. The only downside then is that
> it can't be a module, but I would guess that we can work on making that
> possible by allowing smp ops to be inserted and removed at any time.

Right, I don't see modular SMP operations happening any time soon,
but it also doesn't seem like a fundamental restriction.

Arnd