On Mon, Sep 14, 2020 at 08:34:03PM +0000, Deucher, Alexander wrote: > FWIW, our newer GPUs have both upstream and downstream ports that are > part of the device. > > Slightly off topic, but does the current pm code handle these cases > correctly? ACPI related power handling doesn't seem to work correctly > for these devices in laptops where the GPU power control is handled by > ACPI. PCIe ports are only suspended to D3 if pci_bridge_d3_possible() in drivers/pci/pci.c returns true. In particular, if the downstream ports are hotplug-capable, they will *not* be suspended to D3 unless "pcie_port_pm=force" is specified on the command line. There was a report of MCEs on Xeon-SP servers if hotplug ports were runtime suspended, hence this rule. Also, non-hotplug ports are not suspended if the BIOS is older than 2015. If the downstream ports are not suspended, by consequence the upstream port above them isn't either. So if the GPU is powered down by an ACPI _PR3 method for the upstream port, that method may not be executed. I think the _PR3 method for GPUs was located in the Root Port's namespace so far. If it's moved to a port below that, then it may be necessary to adjust GPU driver code, e.g. where pci_pr3_present() is called (but that's only called by nouveau and hda_intel.c AFAICS). Thanks, Lukas
