[v4, 1/9] ACPI / PM: Let acpi_dev_pm_detach() return an error code

[Ulf Hansson]

On 17 September 2014 22:10, Dmitry Torokhov <dmitry.torokhov at gmail.com> wrote:
> On Wed, Sep 17, 2014 at 08:25:44PM +0200, Ulf Hansson wrote:
>> On 16 September 2014 01:36, Rafael J. Wysocki <rjw at rjwysocki.net> wrote:
>> > On Monday, September 15, 2014 09:53:59 AM Dmitry Torokhov wrote:
>> >> On Sun, Sep 14, 2014 at 06:38:58PM +0200, Rafael J. Wysocki wrote:
>> >> > On Friday, September 12, 2014 02:05:53 PM Dmitry Torokhov wrote:
>> >> > > Hi Ulf,
>> >> > >
>> >> > > On Tue, Sep 09, 2014 at 01:36:02PM +0200, Ulf Hansson wrote:
>> >> > > > To give callers the option of acting on a errors while removing the
>> >> > > > pm_domain ops for the device in the ACPI PM domain, let
>> >> > > > acpi_dev_pm_detach() return an int to provide the error code.
>> >> > >
>> >> > > So how would callers handle the errors? As far as I can see
>> >> > > acpi_dev_pm_detach() is called from ->remove() and ->shutdown() methods, where
>> >> > > there is no meaningful strategy to handle errors as you are past the point of
>> >> > > no return and you keep on tearing down the device.
>>
>> The benefit is only relevant when ACPI and genpd PM domains would
>> co-exist. In that case we might be able to skip genpd_dev_pm_detach()
>> if acpi_dev_pm_detach() succeeds. So, currently there are  no benefit,
>> but still it doesn't hurt.
>
> It doe snot have any negative material effect, the drawback is purely
> from API perspective.
>
>>
>> >> >
>> >> > This is specifically for what patch [3/9] is doing AFAICS.
>> >> >
>> >> > The existing callers don't need to worry about this.
>> >>
>> >> OK, so I have the very same comment about patch 3 then: we have
>> >> dev_pm_domain_detach() returning error. How would the callers handle errors?
>> >
>> > Ulf?
>>
>> I see your point. How about making dev_pm_domain_detach() to be a void
>> function instead?
>
> Yes, please.

OK!

>
>>
>> >
>> >> WRT this patch: I'd rater we did not just return generic "error code" just
>> >> because we do not know who manages PD for the device. Can we add API to check
>> >> if we are using ACPI to manage power domains? Then patch #3 could check if it
>> >> needs to use ACPI or generic power domain API.
>>
>> The problem is scalability. If we have other PM domains implementation
>> in future, each of them need to be checked prior invoking the attach
>> functions.
>> Also, how would we distinguish between genpd and a new PM domain XYZ?
>
> I do not think that trying all available methods to detach a pm domain,
> i.e.
>
>         err = acpi_dev_pm_detach();
>         if (err)
>                 err = blah_dev_pm_detach();
>         if (err)
>                 err = flab_dev_pm_detach();
>         if (err)
>                 err = gen_dev_pm_detach();
>
> is any better from scalability point of view. If you need to do that you
> will probably have to store something like "struct pd_ops *pd_ops" in
> your device and call appropriate implementation via it.

No, that's not needed. Go ahead and have look at both ACPI and genpd,
the interesting part is the validation of struct dev_pm_domain pointer
in the struct device. That's all there is to it, no additional data
are required.

Kind regards
Uffe