A GPU that can switch off but cannot wake again is not usable hybrid graphics. The MacBookPro15,1 patch series addresses that missing return path, with a carefully limited hardware scope.
The proposal and its current status
The August 12 v3 series spans apple-gmux, amdgpu and the audio controller. Its author reports successful offload, monitor and suspend tests on 2018 and 2019 MacBookPro15,1 machines, with roughly 24 W idle draw before the change and about 12 W attributed to the unused discrete GPU. These are contributor measurements, not our tests or a guarantee for all MacBooks.
The specific new power sequence is absent from the v7.3-rc2 apple-gmux source checked for this revision. Treat the series as proposed work, not a feature established in that mainline release candidate. A downstream kernel may carry its own patches.
Three participants share the transition
The kernel’s switcheroo documentation explains that a discrete GPU’s HDMI/DisplayPort audio device participates in power management. Audio use can require the GPU to remain awake. Firmware power control, graphics-driver state and audio dependencies must therefore agree.
Our cover follows a conceptual cycle: integrated GPU handles the desktop; the discrete card wakes for work or a connected output; after its users release it, it can become idle again. Turning it off once tests only one arrow. Repeated wakeups, external-display audio and system resume exercise different parts of the cycle.
Watts do not directly give hours
For a purely hypothetical 60 Wh usable battery, a constant 24 W load gives 2.5 hours, while 12 W gives five. That arithmetic assumes the whole machine actually stays at those loads. It is not a runtime prediction for the tested laptops: battery wear, display brightness and active workloads change the denominator.
Before attributing a personal machine’s result to this series, record its exact model identifier, kernel build and graphics configuration. Compare the same idle conditions and then test the operations that need the second GPU. A large saving in one idle state is valuable evidence, but it does not certify the complete laptop power lifecycle.
Limit hardware to MacBookPro15,1 and measurements to author tests; check v7.3-rc2 source rather than claiming mainstream delivery.