Ubuntu – ACPI PPC Probe failed. Starting version 219 NVIDIA

I believe the 'ACPI PCC probe failed' is a separate issue from your display brightness. I base this hypothesis on the following:

1. http://permalink.gmane.org/gmane.linux.power-management.general/56400
2. Similarly: http://comments.gmane.org/gmane.linux.acpi.devel/73411
3. You have stated you no longer see the 'ACPI' message after you upgraded
4. You still see 'Starting Version 219'
5. The boot process is controlled by 'Systemd' current version 219
6. I see 'ACPI PCC probe failed starting version 219' only after a previously hibernated or suspended session has been resumed and then rebooted, or shutdown and then started
7. There are many questions on AskUbuntu and many other sites regarding this message and each seem to have a different set of repeatable steps to replicate the message
8. The 'ACPI' message is a bug: https://bugzilla.kernel.org/show_bug.cgi?id=92551

My research shows that the kernel is looking for the Platform Communications Channel Interface which is a new ACPI interface that not too many devices support yet. The error return messages are PCCT header not found. followed by ACPI PCC probe failed. Per Ashwin Chaugule code creator found here https://github.com/torvalds/linux/blob/master/drivers/mailbox/pcc.c

My relevant journalctl output

sodu journalctl

Aug 16 23:10:55 x kernel: PCCT header not found.

Aug 16 23:10:55 x kernel: ACPI PCC probe failed.

In all I think there are too many variables for so many seeing the same message. Statistically this makes your unique issue a higher probability that it is unrelated to your display brightness controls. Further, if you read the emails completely in the first two points in the list above I think it is clear that a work around was developed inside the code the developers created that would be attended in the future for upstream releases.

I know this does not completely answer your issue but I am hoping it will focus others with more Linux Ubuntu 15.04 knowledge and experience to a solution or a working hypothesis to resolve it.

I did receive this "ACPI PCC probe failed; starting version 219" error as soon as I received the latest version of Ubuntu (15.04) with the generic kernel 3.19. ???. As soon as I rebooted my laptop the screen went blank (or a black screen) and the laptop just "hung" and would not proceed further. The only option for me was to power off and then power on. Upon booting, Ubuntu went to the " "advanced ubuntu options" in GRUB " and by selecting the prior available kernel 3.18. ??, my laptop booted successfully and was quite usable as before.

As from April 23, 2015 until this morning, May 20, 2015, I had to use the ... power on, power off, power on, select the kernel 3.18. ?? to use my laptop ... . On the morning of May 20, 2015, Ubuntu made availble the latest Kernel 3.19.0.18 to download and now my laptop boots up properly as before with no errors.

As is the same with Microsoft Windows, the developers at Ubuntu must always update their operating systems and sometimes minor things do get missed.

My laptop is a Dell Inspiron B120 with a "Intel® Celeron(R) M processor 1.40GHz", "Intel® 915GM x86/MMX/SSE2" graphics card, 32 bit processor, and 2 Gigabyte RAM. It is a solid laptop but struggles with Windows as Windows can be quite hefty on older laptops which is why I chose Ubuntu as it is really quite a light operating system that offers similar functionality as Windows.

I appreciate Ubuntu very much and hopefully, future upgrades will explain a little more clearly some missed errors whether critical or not.

Anyway, I understand the tribulations for the operating systems programmers and the effort required to update operating systems to keep them secure.

I wish them well.