Re: [RFC PATCH 01/13] device property: Add cleanup.h based fwnode_handle_put() scope based cleanup.

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Sun, 7 Jan 2024 22:05:35 +0100
Rasmus Villemoes <linux@rasmusvillemoes.dk> wrote:

> On 06/01/2024 18.53, Jonathan Cameron wrote:
> > 
> > ething similar and PeterZ explained there why if (_T) is  
> >> important, hence this should be  
> > 
> > I can't find the reference unfortunately. 
> >   
> >>
> >> DEFINE_FREE(fwnode_handle, struct fwnode_handle *, if (_T) fwnode_handle_put(_T))
> >>
> >> or even
> >>
> >> DEFINE_FREE(fwnode_handle, struct fwnode_handle *, if (!IS_ERR_OR_NULL(_T)) fwnode_handle_put(_T))
> >>
> >> as we accept in many calls an error pointer as unset / undefined firmware node
> >> handle.  
> > 
> > The function called has a protection for null
> >  and error inputs so I'm not sure why extra protection
> > is needed?  
> 
> IIRC, it's for code generation, avoiding emitting the call to the
> cleanup function on the code paths where the compiler knows the argument
> is NULL. And on the other return paths, the compiler most likely knows
> the value is non-NULL, so the conditional is elided (but of course not
> the put call). Read ERR_OR_NULL as appropriate.
> 
> Rasmus
> 
> 

Thanks. Makes sense.  A reference in another thread where this was being discussed
lead me to a reference to Linus arguing for just this:
https://lore.kernel.org/all/20230814161731.GN776869@hirez.programming.kicks-ass.net/