Re: [PATCH] PM / Domains: If an OF node is found but no device probed yet, defer.

[Kevin Hilman <khilman@kernel.org>]

Geert Uytterhoeven <geert@linux-m68k.org> writes:

> On Wed, Mar 11, 2015 at 11:08 PM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>> More CCes.
>>
>> On Wednesday, March 11, 2015 08:27:28 AM Eric Anholt wrote:
>>> If we've declared a power domain in the OF, and the OF node is found
>>> but the requested domain hasn't been registered on it yet, then we
>>> probably have just tried to probe before the power domain driver has.
>>> Defer our device's probe until it shows up.
>>>
>>> Signed-off-by: Eric Anholt <eric@anholt.net>
>>
>> Kevin, Ulf, any chance to have a look at this, please?
>>
>>> ---
>>>
>>> I ran into this when turning my ad-hoc code for BCM2835 (Raspberry Pi)
>>> USB poweron support in the DWC2 controller to an OF-based power domain
>>> declaration.
>
> I guess you are initializing the PM domains from module_init()?
>
> I use core_initcall() in arch/arm/mach-shmobile/pm-rmobile.c to make sure it's
> initialized earlier, as e.g. the interrupt controller uses postcore_initcall().

Yeah, I think most existing users are initizling PM domains early, but IMO
we should be working towards supporting PM domains that are created
later as well (as this patch does.)

>>> drivers/base/power/domain.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
>>> index ba4abbe..2b93c98 100644
>>> --- a/drivers/base/power/domain.c
>>> +++ b/drivers/base/power/domain.c
>>> @@ -2064,7 +2064,7 @@ EXPORT_SYMBOL_GPL(of_genpd_del_provider);
>>>  struct generic_pm_domain *of_genpd_get_from_provider(
>>>                                       struct of_phandle_args *genpdspec)
>>>  {
>>> -     struct generic_pm_domain *genpd = ERR_PTR(-ENOENT);
>>> +     struct generic_pm_domain *genpd = ERR_PTR(-EPROBE_DEFER);
>
> Currently platform_drv_probe() just continues if dev_pm_domain_attach() returns
> a different error than -EPROBE_DEFER, which is what you are seeing.
>
> Your change does have the side effect that a new DT with PM domains won't
> work on an older kernel that doesn't have the PM domain driver yet.

Is that a real problem though?  Using newer DTs on older kernels can
cause many types of problems.

Kevin