[PATCH] PM / Sleep: Fall back to subsystem level PM callbacks for PM domains

[Ulf Hansson]

On 30 April 2014 00:52, Rafael J. Wysocki <rjw at rjwysocki.net> wrote:
> On Wednesday, April 30, 2014 12:47:28 AM Rafael J. Wysocki wrote:
>> On Friday, April 25, 2014 12:44:55 PM Ulf Hansson wrote:
>> > Previously once the PM core found a PM domain pointer for a device,
>> > but which didn't have a valid PM callback, it falled back to try the
>> > driver's PM callback.
>> >
>> > In this scenario, change the behavior of the PM core to try out the
>> > other subsystem level PM callbacks, before it moves on to the driver.
>> >
>> > This gives provision for PM domains to easier re-use subsystem level
>> > code to handle the needed operations.
>> >
>> > Signed-off-by: Ulf Hansson <ulf.hansson at linaro.org>
>>
>> Are you sure this is not going to break the existing PM domains?

I have checked the current implementations of the PM domains - all are
providing the PM callbacks. So this should be safe.

>
> And even if it isn't, the idea behind PM domains was to provide a mechanism to
> bypass the bus types' (etc) PM callbacks, so I'm not liking this patch at all.

I understand your view, it's the current mindset we have of the
hierarchy of handling the callbacks. I am wondering if it's time to
reconsider. :-)

To be clear, I don't want to prevent the PM domain from bypassing bus,
types etc, that's should be up to each implementation to decide, and
this patch won't affect that behaviour.

I intend to only simplify for those PM domains that want to re-use the
callbacks from bus, types. etc. Currently that's the most of them.

a)
Those ARM SOCs that implements PM domains, which don't use the generic
power domain, cares only about platform devices attached to the
platform_bus_type. These are copying the callbacks from the
platform_bus_type (using the USE_PLATFORM_PM_SLEEP_OPS macro)  - I
assume this is because they need to handle legacy suspend/resume.

arch/arm/mach-davinci/pm_domain.c
arch/arm/mach-keystone/pm_domain.c
arch/arm/mach-omap1/pm_bus.c
arch/arm/mach-omap2/omap_device.c
drivers/sh/pm_runtime.c

b)
An actual copy of the bus' PM callbacks to the PM domain's callbacks also exist.

drivers/gpu/vga/vga_switcheroo.c:
vga_switcheroo_init_domain_pm_ops()
vga_switcheroo_init_domain_pm_optimus_hdmi_audio()

c)
That leaves the generic power domain and acpi power domain, which
don't re-use callbacks, but have their own set.


The more complicated scenario have not yet been implemented - but I
can see it coming. :-)
That's when the PM domain wants to re-use callbacks for whatever bus,
types etc, the device is attached to.

To handle this, the PM domain will have to re-implement the code for
walking the hierarchy of callbacks, which is a bit messy. This patch
will make it possible for the PM domain to rely on the PM core to
handle this instead.

Kind regards
Ulf Hansson

>
> Thanks!
>
>
> --
> I speak only for myself.
> Rafael J. Wysocki, Intel Open Source Technology Center.