On Fri, Mar 27, 2020 at 02:16:15PM -0700, Ashok Raj wrote:
> Root Complex Integrated devices (RCiEP) do not have a Root Port before the
> device. pci_configure_mps() should simply stick the max value for MaxPayload
> size in Device Control, and for MaxReadReq. Unless pcie=pcie_bus-peer2peer
> is used in kernel commandline PCIE_BUS_PEER2PEER.
>
> When MPS is configured lower, it could result in reduced performance.
>
> Fixes: 9dae3a97297f ("PCI: Move MPS configuration check to pci_configure_device()")
> Signed-off-by: Ashok Raj <ashok.raj@xxxxxxxxx>
> Tested-by: Dave Jiang <dave.jiang@xxxxxxxxx>
> To: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> To: linux-pci@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: Ashok Raj <ashok.raj@xxxxxxxxx>
Applied to pci/enumeration for v5.8, thanks!
> ---
> drivers/pci/probe.c | 23 ++++++++++++++++++++++-
> 1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index eeff8a07..a738b1c 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1895,13 +1895,34 @@ static void pci_configure_mps(struct pci_dev *dev)
> struct pci_dev *bridge = pci_upstream_bridge(dev);
> int mps, mpss, p_mps, rc;
>
> - if (!pci_is_pcie(dev) || !bridge || !pci_is_pcie(bridge))
> + if (!pci_is_pcie(dev))
> return;
>
> /* MPS and MRRS fields are of type 'RsvdP' for VFs, short-circuit out */
> if (dev->is_virtfn)
> return;
>
> + /*
> + * If this is a Root Complex Integrated Endpoint
> + * Simply program the max value from DEVCAP. No additional
> + * Lookup is necessary
> + */
> + if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END) {
> + if (pcie_bus_config == PCIE_BUS_PEER2PEER)
> + mps = 128;
> + else
> + mps = 128 << dev->pcie_mpss;
> + rc = pcie_set_mps(dev, 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",
> + mps);
> + return;
> + }
> + }
> +
> + if (!bridge || !pci_is_pcie(bridge))
> + return;
> +
> mps = pcie_get_mps(dev);
> p_mps = pcie_get_mps(bridge);
>
> --
> 2.7.4
>
