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authorMattia Dongili <malattia@linux.it>2006-07-06 01:12:20 +0400
committerDave Jones <davej@redhat.com>2006-08-01 02:37:05 +0400
commit9c9a43ed2734081124407c779b36a4761c41139b (patch)
treeb32e4d83e840c46f8ef760bda594d7a02e1c41c9 /drivers/cpufreq/cpufreq.c
parent49b1e3ea19b1c95c2f012b8331ffb3b169e4c042 (diff)
downloadlinux-9c9a43ed2734081124407c779b36a4761c41139b.tar.xz
[CPUFREQ] return error when failing to set minfreq
I just stumbled on this bug/feature, this is how to reproduce it: # echo 450000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq # echo 450000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq # echo powersave > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor # cpufreq-info -p 450000 450000 powersave # echo 1800000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq ; echo $? 0 # cpufreq-info -p 450000 450000 powersave Here it is. The kernel refuses to set a min_freq higher than the max_freq but it allows a max_freq lower than min_freq (lowering min_freq also). This behaviour is pretty straightforward (but undocumented) and it doesn't return an error altough failing to accomplish the requested action (set min_freq). The problem (IMO) is basically that userspace is not allowed to set a full policy atomically while the kernel always does that thus it must enforce an ordering on operations. The attached patch returns -EINVAL if trying to increase frequencies starting from scaling_min_freq and documents the correct ordering of writes. Signed-off-by: Mattia Dongili <malattia@linux.it> Signed-off-by: Dominik Brodowski <linux at dominikbrodowski.net> Signed-off-by: Dave Jones <davej@redhat.com> --
Diffstat (limited to 'drivers/cpufreq/cpufreq.c')
-rw-r--r--drivers/cpufreq/cpufreq.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index bc1088d9b379..ad996c772c8b 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1343,6 +1343,11 @@ static int __cpufreq_set_policy(struct cpufreq_policy *data, struct cpufreq_poli
memcpy(&policy->cpuinfo, &data->cpuinfo, sizeof(struct cpufreq_cpuinfo));
+ if (policy->min > data->min && policy->min > policy->max) {
+ ret = -EINVAL;
+ goto error_out;
+ }
+
/* verify the cpu speed can be set within this limit */
ret = cpufreq_driver->verify(policy);
if (ret)