Lenovo Thinkpad T495

Lenovo Thinkpad T495 is a business notebook based on 2nd generation of AMD Ryzen™ processors with Radeon™ Vega graphics, supporting AMD FreeSync™, and delivering up to 14.9 hours of battery life.

Hardware
Lenovo Thinkpad T495 specification:

CPU and its features:

List of PCI devices:

List of USB devices:

Processor
Using with the   USE flag will have additional Processor family options made available:

or simply autodetecting the processor options by the compiler:

For more information see the wiki page on AMD Ryzen processors.

Firmware
In order for the graphics and wireless to work properly, it is necessary to install the proper firmware (or microcode) files and build them into the kernel, as shown below.

These files should be installed in the system before the kernel recompilation using, for example, the command

See amdgpu and iwlwifi wiki pages for more information.

GRUB settings
Edit/update the following line in the following file:

Unable to write to IOMMU
Sometimes (most of the time) I am getting the following kernel message when booting the system:

Later, in the kernel log, one can find the following line:

It seems that IOMMU works just fine and the first message is a result of a premature initialization of the IOMMU system. According to other reports found on the internet, it can be ignored. Still, it pollutes the screen during a silent boot process.

Slow/unresponsive system after direct reboot from Microsoft Window 10
Since kernel version 5.4, some issues related to MMC/SDHCI occur after rebooting to Gentoo Linux from Microsoft Windows 10. The system becomes slow with a few kernel threads using 100% of CPU. These issues do not occur after clean boot to Gentoo Linux. The issue has been reported (kernel bug [//bugzilla.kernel.org/show_bug.cgi?id=205871 #205871]).