Linux 4.20 Allows Overclockers To Increase The Radeon TDP Power Limit

The AMDGPU Linux kernel driver for a while has now offered command-line-driven OverDrive overclocking for recent generations of Radeon GPUs. This has allowed manipulating the core and memory clock speeds as well as tweaking the voltage but has not supported increasing the TDP limit of the graphics card: that's in place with Linux 4.20

Up until now with the AMDGPU Linux kernel driver there hasn't been support for increasing the TDP power limit beyond its default, but has allowed for reducing that limit should you be trying to conserve power / allow your GPU to run cooler. A change was quietly added to the Linux 4.20 kernel to allow increasing the power limit when in the OverDrive mode.

This change wasn't prominently advertised but fortunately a Phoronix reader happened to run across it today and tipped us off.

Increasing the GPU TDP power limit first requires enabling AMD OverDrive on Linux, which is done via the amdgpu.ppfeaturemask=0xffffffff kernel boot parameter when starting the system. The standard location for reading and setting the TDP power limit is via /sys/class/drm/card0/device/hwmon/hwmon0/power1_cap. But with Linux 4.20+, rather than only being able to lower the limit (or read its current value), it can be increased beyond the default.

The support for bumping up the power limit in OverDrive mode isn't free reign but will only allow increasing up to the TDPODLimit value defined within the graphics card's video BIOS. But for overclocking purposes on most newer graphics cards it should allow for a modest boost to allow pushing the frequencies further with the code.

The rest of the OverDrive functionality is the same, including the lines of /sys/class/drm/card0/device/pp_od_clk_voltage, /sys/class/drm/card0/device/pp_dpm_sclk, and other tunables via sysfs.