https://bugzilla.kernel.org/show_bug.cgi?id=202043
Bug ID: 202043 Summary: amdgpu: Vega 56 SCLK drops to 700 Mhz when undervolting Product: Drivers Version: 2.5 Kernel Version: 4.19.8, 4.20.0-rc6 Hardware: All OS: Linux Tree: Mainline Status: NEW Severity: normal Priority: P1 Component: Video(DRI - non Intel) Assignee: drivers_video-dri@kernel-bugs.osdl.org Reporter: antifermion@protonmail.com Regression: No
When undervolting my Sapphire Pulse Vega 56 by just 1mV, SCLK immediately drops down to 700 Mhz and pstate 1-2 under load (`gputest /test=fur /width=1920 /height=1080`).
Script to undervolt: ``` echo "s 7 1630 1199" > /sys/class/drm/card0/device/pp_od_clk_voltage echo "c" > /sys/class/drm/card0/device/pp_od_clk_voltage ```
Stock voltage would be 1200 on the Vega 64 Bios. The same behavior can be observed with the stock Vega 56 Bios. Undervolting the memory by 1mV results in similar behavior. Overvolting by 1mV has no discernable effect.
`echo r > pp_od_clk_voltage` does not work to go back to the normal behavior. Instead, I need to use `echo "s 7 1630 1200" > pp_od_clk_voltage` as above.
Without undervolting, SCLK is around 1330 Mhz, which matches the behavior on Windows, where undervolting by around 150 mV is no problem and increases clock.
With an increased power limit of 300W, the clocks increase to around 1100 Mhz while the card uses the full 300W. It even maxes that limit with a significant underclock/undervolt which would pull around 200W on Windows.
I tested with current Manjaro (4.19.8-2-MANJARO), as well as Kubuntu 18.10 with stock (4.18) and 4.20 from https://github.com/M-Bab/linux-kernel-amdgpu-binaries.