SRU Justification:
Impact: upon boot, frequency scaling is not working.
Fix: Apply the patches, recompile and reboot.
Testcase: Try booting a beaglebone with and without a patched kernel.
With this series applied there should be:
ubuntu@beaglebone:~$ ls -la /sys/devices/system/cpu/cpu0/cpufreq/
total 0
drwxr-xr-x 3 root root 0 May 22 07:03 .
drwxr-xr-x 5 root root 0 May 22 07:03 ..
-r--r--r-- 1 root root 4096 May 22 07:03 affected_cpus
-r-------- 1 root root 4096 May 22 07:03 cpuinfo_cur_freq
-r--r--r-- 1 root root 4096 May 22 07:03 cpuinfo_max_freq
-r--r--r-- 1 root root 4096 May 22 07:03 cpuinfo_min_freq
-r--r--r-- 1 root root 4096 May 22 07:03 cpuinfo_transition_latency
-r--r--r-- 1 root root 4096 May 22 07:03 related_cpus
-r--r--r-- 1 root root 4096 May 22 07:03 scaling_available_frequencies
-r--r--r-- 1 root root 4096 May 22 07:03 scaling_available_governors
-r--r--r-- 1 root root 4096 May 22 07:03 scaling_cur_freq
-r--r--r-- 1 root root 4096 May 22 07:03 scaling_driver
-rw-r--r-- 1 root root 4096 May 22 04:43 scaling_governor
-rw-r--r-- 1 root root 4096 May 22 07:03 scaling_max_freq
-rw-r--r-- 1 root root 4096 May 22 07:03 scaling_min_freq
-rw-r--r-- 1 root root 4096 May 22 07:03 scaling_setspeed
drwxr-xr-x 2 root root 0 May 22 07:03 stats
ubuntu@beaglebone:~$
With an unpatched kernel, until the cpufreq module is loaded, that directory doesn't exist.
...
While cpufreq support on armhf is available for a while, if support is compiled as a kernel module, the corresponding module doesn't autoload by default, and thus frequency scaling is not active upon boot until a user manually load it (or until /etc/modules is modified to forcibly load it).
While in Trusty cpufreq was built-in on armhf, starting with Utopic we made support available as a kernel module, making people think that cpufreq was either broken or missing in their new kernels.
To fix it, revert back that decision and make cpufreq compiled-in again on armhf - it affects Utopic and Vivid kernels.
This patch is for Utopic.