Re: [PATCH 56/62] watchdog: tangox_wdt: Convert to use device managed functions

[Guenter Roeck]

On 01/11/2017 04:31 AM, Marc Gonzalez wrote:
> On 11/01/2017 11:52, Guenter Roeck wrote:
>
> > On 01/11/2017 01:07 AM, Marc Gonzalez wrote:
> >
> > > > @@ -134,12 +134,15 @@ static int tangox_wdt_probe(struct platform_device *pdev)
> > > >  	err = clk_prepare_enable(dev->clk);
> > > >  	if (err)
> > > >  		return err;
> > > > +	err = devm_add_action_or_reset(&pdev->dev,
> > > > +				       (void(*)(void *))clk_disable_unprepare,
> > > > +				       dev->clk);
> > > > +	if (err)
> > > > +		return err;
> > >
> > > Hello Guenter,
> > >
> > > I would rather avoid the function pointer cast.
> > > How about defining an auxiliary function for the cleanup action?
> > >
> > > clk_disable_unprepare() is static inline, so gcc will have to
> > > define an auxiliary function either way. What do you think?
> >
> > Not really. It would just make it more complicated to replace the
> > call with devm_clk_prepare_enable(), should it ever find its way
> > into the light of day.
>
> More complicated, because the cleanup function will have to be deleted later?
> The compiler will warn if someone forgets to do that.
>
> In my opinion, it's not a good idea to rely on the fact that casting
> void(*)(struct clk *clk) to void(*)(void *) is likely to work as expected
> on most platforms. (It has undefined behavior, strictly speaking.)
I do hear that you object to this code.

However, I must admit that you completely lost me here. It is a cast from
one function pointer to another, passed as argument to another function,
with a secondary cast of its argument from a typed pointer to a void pointer.
I don't think C permits for "undefined behavior, strictly speaking".
Besides, that same mechanism is already used elsewhere, which is how I
got the idea. Are you claiming that there are situations where it won't
work ?

> Do you really dislike the portable solution I suggested? :-(
It is not more portable than the above. It is more expensive and adds more
code.

Thanks,
Guenter