On Wed, Jul 18, 2018 at 12:51:58PM -0600, Myron Stowe wrote:
> In commit 27d868b5e6cf ("PCI: Set MPS to match upstream bridge"), we made
> sure every device's MPS setting matches its upstream bridge, making it more
> likely that a hot-added device will work in a system with an optimized MPS
> configuration.
>
> Recently I've started encountering systems where the endpoint device's MPSS
> capability is less than its root port's current MPS value, thus the
> endpoint is not capable of matching its upstream bridge's MPS setting (see:
> bugzilla via "Link:" below). This leaves the system vunerable - the
> upstream root port could respond with larger sized TLPs than the endpoint
> can handle, and the endpoint will consider them to be 'Malformed'.
>
> One could use the "pci=pcie_bus_safe" kernel parameter to resolve the
> issue, but, it both forces a user to have to supply a kernel parameter to
> get the system to function reliable, and may end up limiting MPS settings
> of other, non-related, sub-topologies which could benefit from maintaining
> their larger values.
>
> This patch augments Keith's approach to include tuning down a root port's
> MPS setting when its hot-added endpoint device is not capable of matching
> it. The tuning down, so that both the root port and endpoint match, is
> limited to root ports with downstream endpoint device sub-topologies.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=200527
> Cc: Keith Busch <keith.busch@xxxxxxxxx>
> Cc: Jon Mason <jdmason@xxxxxxxx>
> Cc: Sinan Kaya <okaya@xxxxxxxxxx>
> Signed-off-by: Myron Stowe <myron.stowe@xxxxxxxxxx>
Applied to pci/enumeration for v4.19, thanks!
> ---
> drivers/pci/probe.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index ac91b6f..2987bd9 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1670,7 +1670,7 @@ 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, rc;
> + int mps, mpss, p_mps, rc;
>
> if (!pci_is_pcie(dev) || !bridge || !pci_is_pcie(bridge))
> return;
> @@ -1694,6 +1694,14 @@ static void pci_configure_mps(struct pci_dev *dev)
> if (pcie_bus_config != PCIE_BUS_DEFAULT)
> return;
>
> + mpss = 128 << dev->pcie_mpss;
> + if (mpss < p_mps && pci_pcie_type(bridge) == PCI_EXP_TYPE_ROOT_PORT) {
> + pcie_set_mps(bridge, mpss);
> + pci_info(dev, "Upstream bridge's Max Payload Size set to %d (was %d, max %d)\n",
> + mpss, p_mps, 128 << bridge->pcie_mpss);
> + p_mps = pcie_get_mps(bridge);
> + }
> +
> 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",
> @@ -1702,7 +1710,7 @@ static void pci_configure_mps(struct pci_dev *dev)
> }
>
> pci_info(dev, "Max Payload Size set to %d (was %d, max %d)\n",
> - p_mps, mps, 128 << dev->pcie_mpss);
> + p_mps, mps, mpss);
> }
>
> static struct hpp_type0 pci_default_type0 = {
>
