On Thu, Feb 22, 2024 at 10:40:52AM +0100, Lukas Wunner wrote: > On Wed, Feb 21, 2024 at 12:20:00PM -0600, Bjorn Helgaas wrote: > > 1) D3hot doesn't work per spec. This sounds like a hardware > > defect in the device that should be a quirk based on > > Vendor/Device ID, not something in DT. I don't actually know if > > this is common, although there are several existing quirks that > > mention issues with D3. > > My recollection is that putting Root Ports into D3hot on older x86 > systems would raise MCEs, which is why pci_bridge_d3_possible() only > allows D3hot in cases which are known to work (e.g. Thunderbolt > controllers, machines with a recent BIOS). It was a conservative > policy chosen to avoid regressions. > So pci_bridge_d3_possible() is only checking for D3hot capability? If so, I'd rename it to pci_bridge_d3hot_possible() and also 'bridge_d3' to 'bridge_d3hot' to make it explicit. Since the default value of 'd3cold_allowed' is true, I believe the code expects all devices to support D0 and D3cold. Please correct me if I'm wrong. - Mani > I don't know if similar issues exist on non-ACPI systems. If they > don't exist, platform_pci_bridge_d3() could just return true for > all devicetree-based systems. Might be worth testing if any systems > can be found which exhibit issues with such a policy. That would > obviate the need to specify "supports-d3" in the devicetree. > Quite the opposite, ports which are known not to work could be > blacklisted. Of course if it turns out that's the majority then > whitelisting via "supports-d3" is a better option. > > > > 2) The platform doesn't support putting the bridge in D3cold and > > back to D0. I don't understand this either because I assumed DT > > would describe *hardware*, and "supports-d3" might imply the > > presence of hardware power control, but doesn't tell us how to > > operate it, and it must be up to a native driver to know how to > > do it. > > I think we're putting devices into D3hot first before cutting power > (i.e. putting them into D3cold), so knowing that D3hot is safe is > basically a prerequisite for D3cold. > > Thanks, > > Lukas -- மணிவண்ணன் சதாசிவம்
