[2/3] PCI: Set MPS to match upstream bridge

From: Keith Busch <keith.busch@intel.com>

Firmware typically configures the PCIe fabric with a consistent Max Payload
Size setting based on the devices present at boot.  A hot-added device
typically has the power-on default MPS setting (128 bytes), which may not
match the fabric.

When adding a new device via pci_device_add(), set its Max Payload Size to
match the upstream bridge (unless PCIe bus tuning is disabled).  Note that
pcie_bus_configure_settings() may further change MPS based on the tuning
policy.

This makes it more likely that a hot-added device will work in a system
with optimized MPS configuration.

If we hot-add a device that only supports 128-byte MPS, it still likely
won't work because we don't reconfigure the rest of the fabric.  Booting
with "pci=pcie_bus_peer2peer" is a workaround for this because it sets MPS
to 128 for everything.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/probe.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)


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On Fri, Aug 21, 2015 at 8:07 AM, Bjorn Helgaas <bhelgaas@google.com> wrote:
> From: Keith Busch <keith.busch@intel.com>
>
> Firmware typically configures the PCIe fabric with a consistent Max Payload
> Size setting based on the devices present at boot.  A hot-added device
> typically has the power-on default MPS setting (128 bytes), which may not
> match the fabric.
>
> When adding a new device via pci_device_add(), set its Max Payload Size to
> match the upstream bridge (unless PCIe bus tuning is disabled).  Note that
> pcie_bus_configure_settings() may further change MPS based on the tuning
> policy.
>
> This makes it more likely that a hot-added device will work in a system
> with optimized MPS configuration.
>
> If we hot-add a device that only supports 128-byte MPS, it still likely
> won't work because we don't reconfigure the rest of the fabric.  Booting
> with "pci=pcie_bus_peer2peer" is a workaround for this because it sets MPS
> to 128 for everything.
>
> Signed-off-by: Keith Busch <keith.busch@intel.com>
> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> ---
>  drivers/pci/probe.c |   12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index eb32395..f73dd7a 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1278,7 +1278,7 @@ int pci_setup_device(struct pci_dev *dev)
>  static void pci_configure_mps(struct pci_dev *dev)
>  {
>         struct pci_dev *bridge = pci_upstream_bridge(dev);
> -       int mps, p_mps;
> +       int mps, p_mps, rc;
>
>         if (!pci_is_pcie(dev) || !bridge || !pci_is_pcie(bridge))
>                 return;
> @@ -1294,6 +1294,16 @@ static void pci_configure_mps(struct pci_dev *dev)
>                          mps, pci_name(bridge), p_mps);
>                 return;
>         }
> +

you may need add if the pcie_bus_config == PCIE_BUS_DEFAULT here.

we should not  could set mps extra for _SAFE, _PERFORMANCE, _PEER2PEER

other than that.

For those patches:
Acked-by: Yinghai Lu <yinghai@kernel.org>

> +       rc = pcie_set_mps(dev, p_mps);
> +       if (rc) {
> +               dev_warn(&dev->dev, "can't set Max Payload Size to %d; if necessary, use \"pci=pcie_bus_safe\" and report a bug\n",
> +                        p_mps);
> +               return;
> +       }
> +
> +       dev_info(&dev->dev, "Max Payload Size set to %d (was %d, max %d)\n",
> +                p_mps, mps, 128 << dev->pcie_mpss);
>  }
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