Re: [PATCH v2 RESEND 1/1] PCI: pcie_bus_config can be set at build time

[Bjorn Helgaas]

On Tue, Feb 24, 2026 at 04:10:17PM -0500, Jim Quinlan wrote:
> On Fri, Feb 20, 2026 at 5:11 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> 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 <james.quinlan@xxxxxxxxxxxx>
> >
> > 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?

I assume there's no hotplug in this setup, so we don't't have to worry
about adding new devices at runtime.  Do you know if there's any
P2PDMA usage?