sysfs files under /sys/devices/system/cpu/cpufreq/ disappear after upgrading kernel

[Gavin Lin]

sysfs files under /sys/devices/system/cpu/cpufreq/ disappear after upgrading kernel.
Kernel: Linux dragon410c 4.15.0-1071-snapdragon #78-Ubuntu SMP Thu Jan 16 22:30:28 UTC 2020 aarch64 aarch64 aarch64 GNU/Linux

Steps:
1. Flash following image and boot the DUT
   https://people.canonical.com/~ppisati/ubuntu_embedded/ubuntu-embedded-18.04-dragon410c.img.xz
2. Enable proposed repository
3. Upgrade kernel to 4.15.0-1071
4. Reboot
5. Check file in /sys/devices/system/cpu/cpufreq/

Expected result:
Files are still there after upgrading kernel.

Actual result:
Files under /sys/devices/system/cpu/cpufreq/ disappear after upgrading kernel.

Hardware infomation:
Dragonboard 410c
ip address: 10.101.51.17

[dann frazier (dannf)]

I can reproduce on 4.15.0-107.73, the current -updates kernel:
ubuntu@dragon410c:~$ ls /sys/devices/system/cpu/cpufreq/
ubuntu@dragon410c:~$
So this is not a regression with current -proposed.

With 4.15.0-45.48 (the one from the ppisati image):
ubuntu@dragon410c:~$ ls /sys/devices/system/cpu/cpufreq/
ondemand policy0

[dann frazier (dannf)]

Correction: that should be 4.15.0-1070.73.

4.15.0-1053.57, which appears to be the oldest one in the archive, *does* have those files.

[dann frazier (dannf)]

1057.62 has them, 1058.64 does not.

I noticed that 1057.62 has only the performance governor built-in, and 1058.64 only has the on-demand governor built-in.

ubuntu@dragon410c:~$ grep CPU_FREQ_DEFAULT_GOV /boot/config-4.15.0-1057-snapdragon /boot/config-4.15.0-1058-snapdragon
/boot/config-4.15.0-1057-snapdragon:# CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE is not set
/boot/config-4.15.0-1057-snapdragon:# CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND is not set
/boot/config-4.15.0-1057-snapdragon:CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE=y
/boot/config-4.15.0-1057-snapdragon:# CONFIG_CPU_FREQ_DEFAULT_GOV_POWERSAVE is not set
/boot/config-4.15.0-1057-snapdragon:# CONFIG_CPU_FREQ_DEFAULT_GOV_SCHEDUTIL is not set
/boot/config-4.15.0-1057-snapdragon:# CONFIG_CPU_FREQ_DEFAULT_GOV_USERSPACE is not set
/boot/config-4.15.0-1058-snapdragon:# CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE is not set
/boot/config-4.15.0-1058-snapdragon:CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND=y
/boot/config-4.15.0-1058-snapdragon:# CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE is not set
/boot/config-4.15.0-1058-snapdragon:# CONFIG_CPU_FREQ_DEFAULT_GOV_POWERSAVE is not set
/boot/config-4.15.0-1058-snapdragon:# CONFIG_CPU_FREQ_DEFAULT_GOV_SCHEDUTIL is not set
/boot/config-4.15.0-1058-snapdragon:# CONFIG_CPU_FREQ_DEFAULT_GOV_USERSPACE is not set

[dann frazier (dannf)]

My $0.02 is that we should mark this Invalid. We appear to have intentionally changed the governor, and that new governor does not expose the attributes that the old one did. @Gavin: is this causing any issue for you, or is it just something your testing noticed?

[Gavin Lin (gavin.lin)]

This caused a test(which checks that file) failed:
https://certification.canonical.com/hardware/201901-26783/submission/159672/test/103/result/12095149/

But I didn't see any function lost, so it's fine since we changed it intentionally.