Public bug reported:

[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

[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 --
[   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

-- after kernel patch --

** Affects: linux (Ubuntu)
     Importance: High
     Assignee: Canonical Kernel Team (canonical-kernel-team)
         Status: New


** Tags: starbuck

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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:
  New

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

  [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 --
  [   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

  -- after kernel patch --

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