Re: [PATCH V2] cpufreq: Correct a freq check in cpufreq_set_policy

[Rafael J. Wysocki]

On Thursday, July 30, 2015 06:10:40 PM Pan Xinhui wrote:
> From: Pan Xinhui <xinhuix.pan@xxxxxxxxx>
> 
> This check was originally added by commit 9c9a43ed2734 ("[CPUFREQ]
> return error when failing to set minfreq").It attempt to return an error
> on obviously incorrect limits when we echo xxx >.../scaling_max,min_freq
> Actually we just need check if new_policy->min > new_policy->max.
> Because at least one of max/min is copied from cpufreq_get_policy().
> 
> For example, when we echo xxx > .../scaling_min_freq, new_policy is
> copied from policy in cpufreq_get_policy. new_policy->max is same with
> policy->max. new_policy->min is set to a new value.
> 
> Let me explain it in deduction method, first statement in if ():
> new_policy->min > policy->max
> policy->max == new_policy->max
> ==> new_policy->min > new_policy->max
> 
> second statement in if():
> new_policy->max < policy->min
> policy->max < policy->min
> ==>new_policy->min > new_policy->max (induction method)
> 
> So we have proved that we only need check if new_policy->min >
> new_policy->max.
> 
> After apply this patch, we can also modify ->min and ->max at same time
> if new freq range is very much different from current freq range. For
> example, if current freq range is 480000-960000, then we want to set
> this range to 1120000-2240000, we would fail in the past because
> new_policy->min > policy->max. As long as the cpufreq range is valid, we
> has no reason to reject the user. So correct the check to avoid such
> case.
> 
> Signed-off-by: Pan Xinhui <xinhuix.pan@xxxxxxxxx>

Queued up for 4.3, thanks!


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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