On Wed, Jun 28, 2023 at 01:09:49PM +0800, Kai-Heng Feng wrote: > On Wed, Jun 28, 2023 at 4:54 AM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > On Tue, Jun 27, 2023 at 04:35:25PM +0800, Kai-Heng Feng wrote: > > > On Fri, Jun 23, 2023 at 7:06 AM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > > > On Tue, Jun 20, 2023 at 01:36:59PM -0500, Limonciello, Mario wrote: > > It's perfectly fine for the IP to support PCI features that are not > > and can not be enabled in a system design. But I expect that > > strapping or firmware would disable those features so they are not > > advertised in config space. > > > > If BIOS leaves features disabled because they cannot work, but at the > > same time leaves them advertised in config space, I'd say that's a > > BIOS defect. In that case, we should have a DMI quirk or something to > > work around the defect. > > That means most if not all BIOS are defected. > BIOS vendors and ODM never bothered (and probably will not) to change > the capabilities advertised by config space because "it already works > under Windows". This is what seems strange to me. Are you saying that Windows never enables these power-saving features? Or that Windows includes quirks for all these broken BIOSes? Neither idea seems very convincing. > > > So the logic is to ignore the capability and trust the default set > > > by BIOS. > > > > I think limiting ASPM support to whatever BIOS configured at boot-time > > is problematic. I don't think we can assume that all platforms have > > firmware that configures ASPM as aggressively as possible, and > > obviously firmware won't configure hot-added devices at all (in > > general; I know ACPI _HPX can do some of that). > > Totally agree. I was not suggesting to limiting the setting at all. > A boot-time parameter to flip ASPM setting is very useful. If none has > been set, default to BIOS setting. A boot-time parameter for debugging and workarounds is fine. IMO, needing a boot-time parameter in the course of normal operation is not OK. Bjorn
