AMD Energy Driver Booted From The Linux 5.13 Kernel
Written by Michael Larabel in AMD on 29 April 2021 at 09:02 AM EDT. 37 Comments
AMD --
While a lot of new features and improvements have been accumulating for the Linux 5.13 kernel with the ongoing merge window, one of the unfortunate aspects of this new kernel is that the AMD Zen CPU energy driver "amd_energy" is indeed being removed.

It's not being removed as some superior driver is being introduced but rather a disagreement between the upstream kernel maintainer(s) and AMD over the handling of the exposed energy sensors. The situation was laid out earlier this month in AMD Energy Monitoring Driver Slated To Be Removed From The Linux Kernel. Long story short, since last year the AMD Energy sensor information has been limited to root due to the PLATYPUS security vulnerability. HWMON maintainer Guenter Roeck proposed slightly limiting and randomizing the sensor data so it couldn't be used for nefarious purposes but still accurate enough for genuine use-cases and no longer needing to be root-only access. However, AMD engineers didn't like that approach.

With the hardware monitoring subsystem maintainer not wanting the information to be restricted to root-only and AMD not wanting the limiting/randomization approach, Guenter went ahead and removed the driver. That's unfortunate for then losing out on AMD CPU energy data for EPYC processors on Linux 5.13 whether root or not.

Guenter wrote in this week's HWMON pull, "The most notable change is the removal of the amd_energy driver. It was rendered all but unusable by making its attributes privileged-only to work around a security issue. A suggested remedy was rejected by AMD, so the only real solution was to remove the driver. For the future, we'll have to make sure that no privileged-access-only drivers are accepted into the hwmon subsystem in the first place. The hwmon ABI document was updated accordingly."

Hopefully some new solution or compromise can be reached so AMD energy monitoring support can be restored in the mainline kernel.

Aside from stripping out the AMD_Energy driver, the hardware monitoring updates for Linux 5.13 does bring a new driver for FSP-3Y power supplies and a new driver for NZXT Kraken water cooling products. The NZXT Kraken X42 / X52 / X62 / X72 now have sensor monitoring support with the mainline kernel for these all-in-one liquid cooling setups.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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