Re: [PATCH v1 2/2] mfd: intel_soc_pmic_chtwc: Switch from __maybe_unused to pm_sleep_ptr() etc

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Mon, Jun 20, 2022 at 10:38:34AM +0200, Hans de Goede wrote:
> On 6/16/22 19:10, Andy Shevchenko wrote:
> > Letting the compiler remove these functions when the kernel is built
> > without CONFIG_PM_SLEEP support is simpler and less heavier for builds
> > than the use of __maybe_unused attributes.
> > 
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> 
> I don't see how this helps, __maybe_unused only means the compiler should not
> warn AFAIK it is still allowed to remove static globals which are unused
> even of they are marked __maybe_unused ?

__maybe_unused will force compiler to compile and linker to drop the section.
The proposed approach saves resources on build, i.e. it's already compiler that
decides not to compile the code.

> And DEFINE_SIMPLE_DEV_PM_OPS does not mark the dev_pm_ops as
> __maybe_unused where as pm_sleep_ptr() will not reference the struct
> when CONFIG_PM is not set.
> 
> But I guess that the new PTR_IF magic:
> 
> #define PTR_IF(cond, ptr)       ((cond) ? (ptr) : NULL)
> 
> Still counts as referencing the struct so we don't get
> an unused warning and since cond is a const 0 value the compiler
> can optimize things away ?

See above, it's not olny about warning and compiler.


-- 
With Best Regards,
Andy Shevchenko