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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-DetectorID-Processed: b00c1d49-9d2e-4205-b15f-d015386d3d5e On 3/5/26 13:36, Jim Quinlan wrote: > On Mon, Mar 2, 2026 at 7:03 PM Bjorn Helgaas wrote: >> >> On Tue, Feb 24, 2026 at 04:10:17PM -0500, Jim Quinlan wrote: >>> On Fri, Feb 20, 2026 at 5:11 PM Bjorn Helgaas wrote: >>>> On Mon, Sep 28, 2020 at 03:46:51PM -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. >>>>> >>>>> Signed-off-by: Jim Quinlan >>>> >>>> We merged this as b0e85c3c8554 ("PCI: Add Kconfig options for MPS/MRRS >>>> strategy"), which appeared in v5.10. >>>> >>>> In retrospect, I think this might have been a mistake because it >>>> forces a build-time configuration for something that may not be known >>>> at build time and can be set via command-line parameter. >>> ... >> >>>> But I can't find any discussion about it. Did you have a use case >>>> where command line parameters weren't usable? >>> >>> Yes. We have a Cable Modem (CM) customer who can update their Linux >>> version but cannot update their boot loader or its default bootline. >>> FWIW, they only want the option to set pcie_bus_config to >>> PCIE_BUS_SAFE via the .config. >>> ... >> >>> It's a CM product which uses a particular Wifi chip. Recognizing this >>> scenario would have the RC trying to grab the EP's vendor-id (and >>> possibly more info), and that seems awkward at best. >> >> This is actually kind of weird. I don't know why a particular device >> would have any special MPS or MRRS requirements. >> >> Do you have any more details about this? Does the WiFi chip actually >> not *work* with other MPS settings? Or is this a performance thing >> where other settings don't give acceptable performance? > > Hi Bjorn, > I looked up the original request mail thread on this -- it appears > that the device defaulted to an MPS value of 128, and that value is > what it was assigned. Unfortunately, this device has an occasional HW > bug when MPS=128. Rather than fix the HW bug, they wanted a SW change > in Linux, and somehow that request morphed into a request for > PCIE_BUS_XXX config settings. So the reason for the original > submission is weak and we should have done something different, but > here we are. Late to the party and probably could have suggested back then, but this seems like a prime candidate for using a PCI quirk fixup? -- Florian