Re: [Linux-kernel-mentees] [PATCH v1 2/2] realtek/8139cp: Remove Legacy Power Management

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Apr 24, 2020 at 07:34:50PM +0530, Vaibhav Gupta wrote:
> > >
> > > But in case of "__maybe_unused", we don't keep a check while binding
> > > ".driver.pm".
> > > Hence, if CONFIG_PM_SLEEP is not defined, still the ".driver.pm" is
> > > bind with a structure
> > > with some random initial values.
> > >
> > > We can use the mix of both?
> > > __maybe_unused xyz_suspend(){}
> > > __maybe_unused xyz_resume(){}
> > > ...
> > > #ifdef CONFIG_PM_SLEEP
> > > .driver.pm = &xyz_pm_ops;
> > > #endif
> >
> > I don't think we need the mix because when CONFIG_PM_SLEEP isn't
> > defined, SIMPLE_DEV_PM_OPS() compiles to:
> >
> >   const struct dev_pm_ops xyz_pm_ops = { }
> >
> > and the xyz_pm_ops struct should be zero-filled.  The #ifdef around
> > ".driver.pm = &xyz_pm_ops" doesn't buy us anything -- the space for
> > the driver.pm pointer is there regardless, so we don't save any space,
> > and the default initialization is zero-filled, so the result is the
> > same.
> 
> Then, I guess my step to remove "#ifdef CONFIG_PM" won't go complete
> waste, I should just use "__maybe_unused" with suspend() and resume()
> to suppress warnings. Right?

Yes, that's what I'd do.  This is all window dressing; the important
thing is getting the semantic change right, i.e., the transformations
of the xyz_suspend() and xyz_resume() functions.  This #ifdef and
__maybe_unused stuff can be trivially changed if necessary.

Bjorn
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