https://bugzilla.kernel.org/show_bug.cgi?id=60839 Bug ID: 60839 Summary: scaling_max_freq cannot be set to values larger than bios_limit Product: Power Management Version: 2.5 Kernel Version: 3.10.10 Hardware: All OS: Linux Tree: Mainline Status: NEW Severity: normal Priority: P1 Component: cpufreq Assignee: cpufreq@xxxxxxxxxxxxxxx Reporter: sven.koehler@xxxxxxxxx Regression: No Background: On my Dell Latitude E6410, the following happens if the power supply is plugged in or plugged out: The value of bios_limit drops for all CPUs to cpuinfo_min_freq. Within seconds, it is then gradually increased until bios_limit is equal to cpuinfo_max_freq. I assume, that this serves the purpose of detecting the type of attached power supply. The BIOS temporarely limits the CPU frequency in order to keep the power consumption low until it is determined that the power supply is the correct one. Problem description: Assume that nobody is writing to scaling_max_freq and that scaling_max_freq=cpuinfo_max_freq initially. Upon switching the power supply, you observe that the value of scaling_max_freq decreases and then gradually increases along with bios_limit. From this I conclude that (a) internally, the value for scaling_max_freq can assume values larger than bios_limit. However, when reading scaling_max_freq through sysfs the value is clipped by bios_limit (b) there is no good reason, why the internal value of scaling_max_freq shouldn't be set to a value larger than bios_limit. However, any write to scaling_max_freq through sysfs will also be clipped by bios_limit. In result, if the value of cpuinfo_max_freq is written to scaling_max_freq while bios_limit is low, then the internal value of scaling_max_freq will be set to whatever the value of bios_limit is. In my case, this was causing the following problems: laptop-mode-tools would write to scaling_max_freq shortly after the power supply was plugged in / unplugged. As the bios_limit would be low at that point, the internal value of scaling_max_freq would be set to a low value. Hence, cpufreq would never raise the frequencies of my CPUs again even after bios_limit increased. I solved it my disabling the cpufreq related parts of laptop-mode-tools. Also note, that it isn't currently possible to determine the true value of scaling_max_freq as the value returned through sysfs is clipped by bios_limit. -- You are receiving this mail because: You are the assignee for the bug. -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
