"ACPI PCC probe failed" message is an error message when it should be debug

[Colin Ian King]

[SRU Justification][Vivid]

Users of Ubuntu Vivid are seeing a seemingly alarming kernel failure message "ACPI PCC probe failed" when in fact it is just a debug message informing the kernel developers that a probe for an ACPI PCC mailbox was not successful (which is just a debug only message) and not a failure one needs to worry about. This message is asked about frequently on askubuntu.com, so it is alarming quite a few users, c.f. : http://askubuntu.com/questions/708215/1-037533-acpi-pcc-probe-failed.

This fix landed in Wily, and the driver with the alarming message only affects Vivid.

[Fix]
Upstream commit efd756daf4ddae3cec2404c4e0b680b7cfdd6a45 ("ACPI / PCC: Use pr_debug() for debug messages in pcc_init()")

[Testcase]

Boot a machine without the PCC feature, without the fix one sees the error message in the kernel log. With the fix, this error is now a warning. Note: This only affects Vivid.

[Brad Figg (brad-figg)]

This bug is missing log files that will aid in diagnosing the problem. From a terminal window please run:

apport-collect 1524930

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.

[Colin Ian King (colin-king)]

@Max Payne, please don't change the bug status on this bug. Thank you.

[Luis Henriques (henrix)]

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-vivid' to 'verification-done-vivid'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

[Colin Ian King (colin-king)]

Before fix (3.19.0-43-generic):

dmesg | grep "ACPI PCC"
[ 0.777442] ACPI PCC probe failed.

With fix: (3.19.0-46-generic)

dmesg | grep "ACPI PCC"

So verified it is now fixed with the -proposed kernel

[Andy Whitcroft (apw)]

Fix released in 3.19.0-47.53

[Mutlu Can YILMAZ (mtlcnylmz)]

Same problem persists on Trusty.

[Colin Ian King (colin-king)]

Mutlu, can run:

uname -a

and post the result into the bug report.

[Mutlu Can YILMAZ (mtlcnylmz)]

Linux golcuk-G31M-ES2L 3.19.0-49-generic #55~14.04.1-Ubuntu SMP Fri Jan 22 11:24:31 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux