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

[Stephen Boyd <sboyd@codeaurora.org>]

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.

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