Re: [PATCH V3 05/19] OMAP3+: voltage: use IS_ERR_OR_NULL

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Sun, Mar 06, 2011 at 08:15:06AM +0530, Nishanth Menon wrote:
> my_dumb_func(){
> 	struct voltagedomain *vdata = NULL;
> 	if (cpu_is_omap3630()_) {
> 		vdata = omap_voltage_domain_lookup("mpu")
> 	}
> 	/* forgot to add other cpu types or a else case */
> 	/* do other things */
> 	me_volt=omap_voltage_get_nom_volt(vdata);
> 	/* do things with me_volt */
> }
>
> Sorry, but i think the check, even if seems superfluous is sane IMHO.  
> even if the above code worked on 3630, it'd fail on o4/3430 without the  
> check, it can even crash. and given that we've all seen our fair share  
> of developers who develop for one platform without consideration that  
> the rest of the world uses others as well... I do feel cases like above  
> example might infact be a reality.

But normal practice is to check the return value from functions before
it's used.  So:

 my_dumb_func(){
	struct voltagedomain *vdata = NULL;
	if (cpu_is_omap3630()) {
		vdata = omap_voltage_domain_lookup("mpu")
	}
	/* forgot to add other cpu types or a else case */

+	if (!vdata)
+		return some error;

	/* do other things */
	me_volt=omap_voltage_get_nom_volt(vdata);
	/* do things with me_volt */
 }

is the right way to deal with this.  Pushing the primary error checking
down into sub-functions is stupid - where does it stop?  Do you check
me_volt for errors?  Do you get functions which use me_volt to check for
errors from that too?

It's a silly idea.  Put the primary error checking in the function which
gets the return value.  Don't bury it in sub-functions.