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.
Tyler
> drivers/pci/probe.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 17a969942d37..2c5a1aefd9cb 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2034,7 +2034,9 @@ static void pci_configure_mps(struct pci_dev *dev)
> * Fancier MPS configuration is done later by
> * pcie_bus_configure_settings()
> */
> - if (pcie_bus_config != PCIE_BUS_DEFAULT)
> + if (pcie_bus_config != PCIE_BUS_DEFAULT &&
> + pcie_bus_config != PCIE_BUS_SAFE &&
> + pcie_bus_config != PCIE_BUS_PERFORMANCE)
> return;
>
> mpss = 128 << dev->pcie_mpss;
> @@ -2047,7 +2049,7 @@ static void pci_configure_mps(struct pci_dev *dev)
>
> rc = pcie_set_mps(dev, p_mps);
> if (rc) {
> - pci_warn(dev, "can't set Max Payload Size to %d; if necessary, use \"pci=pcie_bus_safe\" and report a bug\n",
> + pci_warn(dev, "can't set Max Payload Size to %d; if necessary, use \"pci=pcie_bus_peer2peer\" and report a bug\n",
> p_mps);
> return;
> }
> --
> 2.17.1
>
