Need help understanding the logic of __cpuidle_set_driver

[AYAN KUMAR HALDER]

>> However, regarding the logic, I have a few doubts -
>>
>> 1. for each cpu in drv->cpumask, if there is already a driver
>> registered, its calling __cpuidle_unset_driver which loops over for
>> each cpu in drv->cpumask again. Isn't it unnecessary to do this nested
>> calls?
>
>
> It is to rollback the previous changes done in the loop.

However, I have two concerns here:-
1.
static inline int __cpuidle_set_driver(struct cpuidle_driver *drv)
{
        int cpu;
        struct cpuidle_driver *tmp = NULL;
        for_each_cpu(cpu, drv->cpumask) {

                tmp = __cpuidle_get_cpu_driver(cpu); /* This would
prevent nesting of loops */
                if ( tmp != NULL ) {
                        if ( tmp == drv )
                              per_cpu(cpuidle_drivers, cpu) = NULL;
                        return -EBUSY;
                }

                per_cpu(cpuidle_drivers, cpu) = drv;
        }

        return 0;
}
Instead of calling __cpuidle_unset_driver() which would loop-over
again for all the cpus , is it not that the above function would be
more efficient.

2. Secondly, if the cpuidle driver to be registered matches to the one
already registered , then why should it be unset instead of leaving it
as it is.


Any views would be highly appreciated.