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PCI: Set MPS to match upstream bridge

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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.

The previous Linux default, in the absence of any "pci=pcie_bus_*" options,
was PCIE_BUS_TUNE_OFF, in which we never touch MPS, even for hot-added
devices.

Add a new default setting, PCIE_BUS_DEFAULT, in which we make sure every
device's MPS setting matches the upstream bridge.  This makes it more
likely that a hot-added device will work in a system with optimized MPS
configuration.

Note that 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.

[bhelgaas: changelog, new default, rework for pci_configure_device() path]
Tested-by: Keith Busch <keith.busch@intel.com>
Tested-by: Jordan Hargrave <jharg93@gmail.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>
This commit is contained in:
Keith Busch
2015-08-24 08:48:16 -05:00
committed by Bjorn Helgaas
parent 9dae3a9729
commit 27d868b5e6
4 changed files with 28 additions and 8 deletions
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9
include/linux/pci.h
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@@ -738,10 +738,11 @@ struct pci_driver {
void pcie_bus_configure_settings(struct pci_bus *bus);
enum pcie_bus_config_types {
PCIE_BUS_TUNE_OFF,
PCIE_BUS_SAFE,
PCIE_BUS_PERFORMANCE,
PCIE_BUS_PEER2PEER,
PCIE_BUS_TUNE_OFF, /* don't touch MPS at all */
PCIE_BUS_DEFAULT, /* ensure MPS matches upstream bridge */
PCIE_BUS_SAFE, /* use largest MPS boot-time devices support */
PCIE_BUS_PERFORMANCE, /* use MPS and MRRS for best performance */
PCIE_BUS_PEER2PEER, /* set MPS = 128 for all devices */
};
extern enum pcie_bus_config_types pcie_bus_config;