Lenovo Thinkpad L540

This article contains information to assist when installing Gentoo on a Lenovo Thinkpad L540.

Unable to shutdown/reboot, irq N:nobody cared (try booting with the "irqpoll" option), system turns dead after resume from hibernation.
It seems that with kernel <4.0 you may have issues halting the system, which will result in hang after message about powering off. With kernel =4.0 you may have no longer such issue but after you resume from hibernation, USB ports may not work at all as well as you may start seeing the message about irq that nobody cared. With kernel =4.1 systems after resume from hibernation turns dead. The apps are semi-responsible but no new process can be spawned, like storage was offline. Booting with `irqpoll` does make the system works as it should.

As of kernel 4.2.0-rc1 the issues with IRQ are no more.

Brightness control does not work
Depends on kernel version, you may need to boot with either acpi_osi=Linux or with empty string acpi_osi=

Random system hangs with possible screen artifacts
Since update to BIOS version J4ET76WW (1.76) random hard-freezes have been experienced. The screen usually is torn apart. Update to BIOS version 1.78 solve the issue. All version from 1.74 to 1.76 are no longer available on the Lenovo page. 1.77 was never public and 1.78 changelog lists only changes from 1.77 to 1.78.