[SRU][BIONIC] after enabling cppc dmesg fills with "ACPI CPPC: PCC check channel failed. Status=0"

[Manoj Iyer]

[Impact]
On ARM64 systems enabling cppccontrol=1 in firmware, the dmesg fills with messages like:
[ 4083.960332] ACPI CPPC: PCC check channel failed. Status=0
[ 4085.546975] ACPI CPPC: PCC check channel failed. Status=0
[ 4113.939921] ACPI CPPC: PCC check channel failed. Status=0
[ 4115.531777] ACPI CPPC: PCC check channel failed. Status=0

We lose any useful data in dmesg and on the console.

[Fix]
upstream commit fixes this issue:
commit 3d41386d556db9f720e00de3e11e45f39cb5071c
Author: George Cherian <email address hidden>
Date: Fri Mar 23 03:30:31 2018 -0700

    cpufreq: CPPC: Use transition_delay_us depending transition_latency

[Testing]
-- before kernel patch --
Both console output and dmesg are filled with the message
ACPI CPPC: PCC check channel failed. Status=0

[ 85.969952] ACPI CPPC: PCC check channel failed. Status=0
[ 81.888445] cloud-init[4810]: Cloud-init v. 18.2 running 'modules:final' at Fri, 13 Apr 2018 19:11:57 +0000. Up 80.71 seconds.
[ 81.888625] cloud-init[4810]: Cloud-init v. 18.2 finished at Fri, 13 Apr 2018 19:11:58 +0000. Datasource DataSourceMAAS [http://10.228.68.5:5240/MAAS/metadata/]. Up 81.69 seconds
[ OK ] Started Execute cloud user/final scripts.
[ OK ] Reached target Cloud-init target.
[ 86.230432] ACPI CPPC: PCC check channel failed. Status=0
[ 86.701943] ACPI CPPC: PCC check channel failed. Status=0
[ 86.773668] ACPI CPPC: PCC check channel failed. Status=0
[ 87.369958] ACPI CPPC: PCC check channel failed. Status=0
[ 87.733361] ACPI CPPC: PCC check channel failed. Status=0
[ 88.207372] ACPI CPPC: PCC check channel failed. Status=0

ubuntu@starbuck:~$ uname -a
Linux starbuck 4.15.0-13-generic #14-Ubuntu SMP Sat Mar 17 13:44:36 UTC 2018 aarch64 aarch64 aarch64 GNU/Linux

-- after kernel patch --
  OK ] Started Apply the settings specified in cloud-config.
         Starting Execute cloud user/final scripts...
[ 67.178425] cloud-init[3688]: Cloud-init v. 18.2 running 'modules:final' at Fri, 13 Apr 2018 20:41:15 +0000. Up 65.98 seconds.
[ 67.200190] cloud-init[3688]: Cloud-init v. 18.2 finished at Fri, 13 Apr 2018 20:41:15 +0000. Datasource DataSourceMAAS [http://10.228.68.5:5240/MAAS/metadata/]. Up 66.83 seconds
[ OK ] Started Execute cloud user/final scripts.
[ OK ] Reached target Cloud-init target.

Ubuntu Bionic Beaver (development branch) starbuck ttyAMA0

starbuck login:

ubuntu@starbuck:~$ uname -a
Linux starbuck 4.15.0-15-generic #16~lp1763817+build.1 SMP Fri Apr 13 19:54:10 UTC 2018 aarch64 aarch64 aarch64 GNU/Linux

[Regression Potential]
None.

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1763817

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Matt Dirba (5qxm)]

I did a clean install of BIONIC via ubuntu-18.04.1-server-arm64.iso on an ARM system and encountered this on first boot. I am happy to send logs but apport-collect states that I am not the owner

[Matt Dirba (5qxm)]

From playing around it appears about 300 seconds after boot.
I was able to recreate this with kernel 4.15.0-29-generic but no longer after running apt upgrade and rebooting to the 4.15.0-36-generic kernel.