On Thu, Sep 10, 2020 at 08:57:10AM -0400, Jim Quinlan wrote: > Hi Bjorn, > > On Wed, Sep 9, 2020 at 10:25 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > > > On Tue, Sep 08, 2020 at 12:32:48PM -0400, Jim Quinlan wrote: > > > The Kconfig is modified so that the pcie_bus_config setting can be done at > > > build time in the same manner as the CONFIG_PCIEASPM_XXXX choice. The > > > pci_bus_config setting may still be overridden by the bootline param. > > > > I guess... I really hate these build-time config settings for both > > ASPM and MPS/MRRS. But Linux just isn't smart or flexible enough to > > do the right thing at run-time, so I guess we're kind of stuck. > > > > I guess you have systems where you need a different default? > > Yes, we've been shipping our kernel with the DEFAULT and since we do > not have FW it is not configured optimally. Some customers have > noticed and I tell them to put 'pci=pcie_bus_safe' on their bootline > but I'd rather have this setting work for all customers as it yields > the option we want. I'm guessing you probably don't have any hotplug slots. Seems like we ought to be able to recognize that and pick pcie_bus_safe automatically. Someday. Maybe that's part of the description: if you have a closed system with no possibility of adding new devices, we can use the largest MPS that's supported by all devices, i.e., pcie_bus_safe. > > It'd be nice if we could put a little more detail in the Kconfig to > > help users choose the correct one. "Ensure MPS matches upstream > > bridge" is *accurate*, but it doesn't really tell me why I would > > choose this rather than a different one. > > IIRC I just copied the comments that were in the bootline settings. > I'm concerned about there being the same comment in two places; sooner > or later someone will update one place and not the other. True. It'd be nice if we at least had *one* place with a useful description. I don't think we have any today. Bjorn
