[PATCH v3] thermal: tango: add resume support

[Arnd Bergmann]

On Monday, July 25, 2016 10:18:22 AM CEST Mason wrote:
> On 23/07/2016 00:00, Kevin Hilman wrote:
> 
> > Mason wrote:
> > 
> >> +#ifdef CONFIG_PM_SLEEP
> >> +static int tango_thermal_resume(struct device *dev)
> >> +{
> >> +    tango_thermal_init(dev_get_drvdata(dev));
> >> +    return 0;
> >> +}
> >> +
> >> +static SIMPLE_DEV_PM_OPS(tango_thermal_pm, NULL, tango_thermal_resume);
> >> +#endif
> > 
> > #else
> > #define tango_thermal_resume NULL
> > #endif

That's what SIMPLE_DEV_PM_OPS does internally already.

> > And then move the SIMPLE_DEV_PM_OPS here...
> 
> Moving the SIMPLE_DEV_PM_OPS macro outside the CONFIG_PM_SLEEP guard
> would unconditionally define a struct dev_pm_ops, which just wastes
> space when CONFIG_PM_SLEEP is undefined (if I'm not mistaken).
> 
> That's why I put SIMPLE_DEV_PM_OPS inside the CONFIG_PM_SLEEP guard.

If you want to avoid the extra few bytes, just use the trick I
suggested:

	.pm = IS_ENABLED(CONFIG_PM_SLEEP) ? &tango_thermal_pm : NULL,

> >> +
> >>  static const struct of_device_id tango_sensor_ids[] = {
> >>      {
> >>              .compatible = "sigma,smp8758-thermal",
> >> @@ -99,6 +115,9 @@ static struct platform_driver tango_thermal_driver = {
> >>      .driver = {
> >>              .name           = "tango-thermal",
> >>              .of_match_table = tango_sensor_ids,
> >> +#ifdef CONFIG_PM_SLEEP
> >> +            .pm             = &tango_thermal_pm,
> >> +#endif
> > 
> > ... which allows you to get rid of the ugly ifdef here.
> > (c.f. CodingStyle, Chapter 20,)
> 
> The previous solution (v2) avoided duplicating the ifdef block,
> but Arnd and Thierry objected to the code. Later, they agreed
> that it should work; but if they didn't catch the code's intent
> at a glance, maybe there is a problem with it anyway.
> 
> What do you think?
> 
> I copied the DEV_PM_OPS "trick" from drivers/thermal/ti-soc-thermal/ti-bandgap.c
> (which was done by Eduardo, a thermal maintainer, so maybe he
> prefers that solution after all? commit 8feaf0ce1a043)

You should basically never have that #ifdef inside of the
platform_driver definition. The normal way to do it is to have
__maybe_unused markers for the functions so gcc can silently drop
them when they are unused, or to have (slightly uglier and easier
to get wrong) #ifdef around the function, but not around the
references, but nowhere else.

The SIMPLE_DEV_PM_OPS macro is suboptimal because it requires the
__maybe_unused tags and because it leaves more data around than
necessary. Feel free to suggest improvements for those macros
(others have tried before and failed because of the hundreds or
thousands of users that exist), just don't try to be extra clever
in your one driver, it would only make it harder for readers to
understand.

	Arnd