diff options
| author | Pan Xinhui <xinhuix.pan@intel.com> | 2015-07-30 10:10:40 (GMT) |
|---|---|---|
| committer | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2015-07-31 21:22:16 (GMT) |
| commit | fba9573b33f8bddd772195c202f6b8ec0751cedd (patch) | |
| tree | b2e0c346c22105ed2dbad0b2afdae7e15365d5ce | |
| parent | fdd320da84c63092fe6e155cb7b8d80f7f765fa9 (diff) | |
| download | linux-fba9573b33f8bddd772195c202f6b8ec0751cedd.tar.xz | |
cpufreq: Correct a freq check in cpufreq_set_policy()
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@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
| -rw-r--r-- | drivers/cpufreq/cpufreq.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 0f4e96f..76a2660 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -2190,7 +2190,11 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy, memcpy(&new_policy->cpuinfo, &policy->cpuinfo, sizeof(policy->cpuinfo)); - if (new_policy->min > policy->max || new_policy->max < policy->min) + /* + * This check works well when we store new min/max freq attributes, + * because new_policy is a copy of policy with one field updated. + */ + if (new_policy->min > new_policy->max) return -EINVAL; /* verify the cpu speed can be set within this limit */ |