On Wed, Oct 19, 2022 at 01:25:59PM -0500, Tyler Hicks wrote:
> On 2022-06-10 23:01:31, Zhiqiang Hou wrote:
> > From: Hou Zhiqiang <Zhiqiang.Hou@xxxxxxx>
> >
> > The commit 27d868b5e6cf ("PCI: Set MPS to match upstream bridge")
>
> Adding Keith, as the author of that commit.
>
> > made the device's MPS matches upstream bridge for PCIE_BUS_DEFAULT
> > mode, so that it's more likely that a hot-added device will work in
> > a system with an optimized MPS configuration.
> >
> > Obviously, the Linux itself optimizes the MPS settings in the
> > PCIE_BUS_SAFE and PCIE_BUS_PERFORMANCE mode, so let's do this also
> > for these modes.
> >
> > Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@xxxxxxx>
> > ---
>
> I wanted to give a little more information about the issue we're seeing.
> We're having trouble retaining the optimized Max Payload Size (MPS)
> value of a PCIe endpoint after hotplug/rescan. In this case,
> `pcie_ports=native` and `pci=pcie_bus_safe` are set on the cmdline and
> we expect the Linux kernel to retain the MPS value. Commit 27d868b5e6cf
> preserved the MPS value when using the default PCIe bus mode
> (PCIE_BUS_DEFAULT) and we're hopeful that this can be extended to other
> modes, as well.
As I recall, the PCIE_BUS_DEFAULT mode was created specifically because
we didn't want to change the behavior of PCIE_BUS_SAFE. What reason do
you have for using that mode, anyway? That's specifically saying not to
retune bridges after the initial scan.
