Public bug reported:
Both FirePro D700 (Tahiti XT, SI) cards in a Mac Pro 6,1 stay at 300 MHz sclk
/ 150 MHz mclk under load on 7.0.0-42-generic. On 7.0.0-38-generic the same
machine ramps to 850/1370 MHz. GPU workloads run
about 4.6x slower. Writing "high" to power_dpm_force_performance_level
returns EINVAL.
The cause is upstream commit e6c5d36756e7 ("drm/amd/pm/si: Fix
updating clock limits from power states"), which came in with
7.0.0-41.41 through "upstream stable patchset 2026-10-05" (LP:
#2169638).
The VBIOS has ATOM_PP_PLATFORM_CAP_HARDWAREDC, so the SMC picks AC/DC from a
GPIO, and on this machine it reads DC. Before the patch the VBIOS had no DC
limits, so the driver copied the AC limits and every
level counted as DC-compatible. The patch fills the DC limits from the
battery power state (300/150 MHz, 825 mV). The performance state levels go up
to 1100 mV, so they are no longer DC-compatible and the
SMC keeps level 0. The driver itself sees ac_power = 1.
I confirmed this on the running 7.0.0-42 kernel with kprobes and with a
manual workaround. Setting PPSMC_SWSTATE_FLAG_DC on the driver state in SMC
SRAM and sending SwitchToSwState brings the card to
850/1370 MHz immediately. Full details and values are in the upstream report:
https://gitlab.freedesktop.org/drm/amd/-/issues/6083
Upstream follow-up ef8cb9dcc7db does not change the DC part, so I
don't expect it to fix this. Not tested on mainline.
Request: revert e6c5d36756e7 in the resolute kernel, or carry the
upstream fix once there is one.
Release: Ubuntu 26.04.1 LTS
Package: linux-image-7.0.0-42-generic 7.0.0-42.42 (version_signature: Ubuntu
7.0.0-42.42-generic 7.0.14)
Last good: 7.0.0-38.38. Bad: 7.0.0-42.42 (7.0.0-41.41 contains the patch too;
not booted here).
Machine: Apple MacPro6,1, Xeon E5-2697 v2, 2x FirePro D700 [1002:6798] subsys
106B:0127/0128, VBIOS 113-C3861XA-028, headless.
Expected: the GPU ramps to 850/1370 MHz under load, as on 7.0.0-38.
Actual: it stays at 300/150 MHz.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Attachment added: "lspci-vnvn.log"
https://bugs.launchpad.net/bugs/2172815/+attachment/6014642/+files/lspci-vnvn.log
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https://bugs.launchpad.net/bugs/2172815
Title:
SI GPUs stuck at lowest DPM level on Mac Pro 2013 since 7.0.0-41
(drm/amd/pm/si: Fix updating clock limits from power states)
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