** Description changed:

  [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 <george.cher...@cavium.com>
  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 
+ 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.

** Changed in: linux (Ubuntu)
     Assignee: Canonical Kernel Team (canonical-kernel-team) => Manoj Iyer 
(manjo)

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https://bugs.launchpad.net/bugs/1763817

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

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  [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 <george.cher...@cavium.com>
  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.

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