Linux 5.5 To Restore Power-Savings For Hybrid Laptops When Not Using The dGPU
Written by Michael Larabel in Linux Kernel on 22 October 2019 at 04:35 AM EDT. 7 Comments
LINUX KERNEL --
On recent kernels when using a laptop with hybrid graphics but not running with the discrete GPU graphics enabled, a regression meant the dGPU never got powered off... Fortunately, for Linux 5.5 -- and potentially to be back-ported after that -- is a change to restore that power-savings.

A change enabling NVIDIA HDA controller support inadvertently left dGPUs powered up when not in use, i.e. where the dGPU is not bound to a driver. When the NVIDIA discrete graphics aren't bound to a driver, the power saving path wasn't being hit where the platform power management could disable power to the GPU.

This was reported as an Ubuntu bug report ultimately back to their Linux 5.0 kernel and noticing the "high power consumption" was happening when the HDA sound driver was loaded. A workaround is to blacklist the HDA codec HDMI driver and Ubuntu's kernel team also spun their own fix for their packaged kernels while the patch is now working its way upstream thanks to Canonical.

The patch with all the details can be found here where it's queued in "for-next" ahead of Linux 5.5's merge window, but potentially after that point we could see it back-ported to the stable series if deemed sufficient.

In other Linux sound driver news, Realtek ALC711 support was a trivial addition and that support now is ready for Linux 5.4 and also is marked for back-porting to current stable series.
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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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