• Yi Yang's avatar
    cpufreq: fix obvious condition statement error · 53391fa2
    Yi Yang authored
    The function __cpufreq_set_policy in file drivers/cpufreq/cpufreq.c
    has a very obvious error:
    
            if (policy->min > data->min && policy->min > policy->max) {
                    ret = -EINVAL;
                    goto error_out;
            }
    
    This condtion statement is wrong because it returns -EINVAL only if
    policy->min is greater than policy->max (in this case,
    "policy->min > data->min" is true for ever.). In fact, it should
    return -EINVAL as well if policy->max is less than data->min.
    
    The correct condition should be:
    
    	if (policy->min > data->max || policy->max < data->min) {
    
    The following test result testifies the above conclusion:
    
    Before applying this patch:
    
    [root@yangyi-dev /]# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
    2394000 1596000
    [root@yangyi-dev /]# echo 1596000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    [root@yangyi-dev /]# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    1596000
    [root@yangyi-dev /]# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
    1596000
    [root@yangyi-dev /]# echo "2000000" > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
    -bash: echo: write error: Invalid argument
    [root@yangyi-dev /]# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
    1596000
    [root@yangyi-dev /]# echo "0" > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    [root@yangyi-dev /]# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    1596000
    [root@yangyi-dev /]# echo "1595000" > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    [root@yangyi-dev /]# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    1596000
    [root@yangyi-dev /]#
    
    After applying this patch:
    
    [root@yangyi-dev /]# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
    2394000 1596000
    [root@yangyi-dev /]# echo 1596000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    [root@yangyi-dev /]# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    1596000
    [root@yangyi-dev /]# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
    1596000
    [root@localhost /]# echo "2000000" > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
    -bash: echo: write error: Invalid argument
    [root@localhost /]# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
    1596000
    [root@localhost /]# echo "0" > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    -bash: echo: write error: Invalid argument
    [root@localhost /]# echo "1595000" > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    -bash: echo: write error: Invalid argument
    [root@localhost /]# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    1596000
    [root@localhost /]# echo "1596000" > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    [root@localhost /]# echo "2394000" > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    [root@localhost /]# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    2394000
    [root@localhost /]
    Signed-off-by: default avatarYi Yang <yi.y.yang@intel.com>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    53391fa2
cpufreq.c 47 KB