AMD Laptops With Radeon dGPU Graphics Receive Fix For Poor Linux Power Management
Written by Michael Larabel in Hardware on 14 October 2020 at 05:49 AM EDT. 16 Comments
HARDWARE --
The kernel power management changes have been sent in for Linux 5.10 with a few items worth pointing out from faster hibernation to fixing power management handling for AMD laptops with both integrated and discrete graphics.

There have been a number of bug reports concerning AMD Renoir laptops with dual AMD GPUs (both integrated and discrete graphics like the RX 5600M) where there are lock-ups on system sleep and high power consumption in general.

Independent Linux developer Lukas Wunner tracked the issue down to discovering that the discrete graphics are never being suspended to a D3cold state. The kernel's existing behavior was only allowing D3cold support for hot-plug ports if they belong to a Thunderbolt device or have an ACPI property to indicate its support. But with these newer AMD laptops not being Thunderbolt-connected or having the ACPI property, the discrete GPU on these laptops is not going into D3cold. The change by Lukas now will assume D3 support if the bridge is power-manageable by ACPI. So this fix isn't specific to AMD but rather the common Linux kernel PCI ACPI code but at least for now newer AMD laptops are known to be the ones benefiting from this change.

The Linux 5.10 power management code also has a rework of CPUfreq statistics collection, support for CPUfreq core setting the frequency scale on the behalf of the drivers, and much faster hibernation/resume thanks to batching of I/O requests.

The power management changes are outlined by this pull request.

Meanwhile on the ACPI side there is a new Intel PCH FIVR participant driver. This new Intel Dynamic Platform and Thermal Framework (DPTF) driver is for the PCH Fully Integrated Voltage Regular (FIVR). This driver ends up controlling the PCH's FIVR frequency based on the DPTF state.
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