From 9c9a43ed2734081124407c779b36a4761c41139b Mon Sep 17 00:00:00 2001 From: Mattia Dongili Date: Wed, 5 Jul 2006 23:12:20 +0200 Subject: [PATCH] [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 Signed-off-by: Dominik Brodowski Signed-off-by: Dave Jones -- --- Documentation/cpu-freq/user-guide.txt | 5 ++++- drivers/cpufreq/cpufreq.c | 5 +++++ 2 files changed, 9 insertions(+), 1 deletion(-) diff --git a/Documentation/cpu-freq/user-guide.txt b/Documentation/cpu-freq/user-guide.txt index 7fedc00..555c8cf 100644 --- a/Documentation/cpu-freq/user-guide.txt +++ b/Documentation/cpu-freq/user-guide.txt @@ -153,10 +153,13 @@ scaling_governor, and by "echoing" the name of another that some governors won't load - they only work on some specific architectures or processors. -scaling_min_freq and +scaling_min_freq and scaling_max_freq show the current "policy limits" (in kHz). By echoing new values into these files, you can change these limits. + NOTE: when setting a policy you need to + first set scaling_max_freq, then + scaling_min_freq. If you have selected the "userspace" governor which allows you to diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index bc1088d..ad996c7 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) -- 1.8.2.3