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PCI: Document MPS parameters pci=pcie_bus_safe, pci=pcie_bus_perf, etc

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Document PCIe bus MPS parameters pcie_bus_tune_off, pcie_bus_safe,
pcie_bus_peer2peer, pcie_bus_perf.

These parameters were introduced by Jon Mason <jdmason@kudzu.us> at commit
5f39e6705 and commit b03e7495a8.

[bhelgaas: mention hot-add for pcie_bus_peer2peer]
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
This commit is contained in:
Yijing Wang 2013-01-30 09:40:52 +08:00 committed by Bjorn Helgaas
parent 8c8803c596
commit fa2387124b
1 changed files with 15 additions and 0 deletions
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Documentation/kernel-parameters.txt
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@ -2227,6 +2227,21 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
This sorting is done to get a device This sorting is done to get a device
order compatible with older (<= 2.4) kernels. order compatible with older (<= 2.4) kernels.
nobfsort Don't sort PCI devices into breadth-first order. nobfsort Don't sort PCI devices into breadth-first order.
pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
tuning and use the BIOS-configured MPS defaults.
pcie_bus_safe Set every device's MPS to the largest value
supported by all devices below the root complex.
pcie_bus_perf Set device MPS to the largest allowable MPS
based on its parent bus. Also set MRRS (Max
Read Request Size) to the largest supported
value (no larger than the MPS that the device
or bus can support) for best performance.
pcie_bus_peer2peer Set every device's MPS to 128B, which
every device is guaranteed to support. This
configuration allows peer-to-peer DMA between
any pair of devices, possibly at the cost of
reduced performance. This also guarantees
that hot-added devices will work.
cbiosize=nn[KMG] The fixed amount of bus space which is cbiosize=nn[KMG] The fixed amount of bus space which is
reserved for the CardBus bridge's IO window. reserved for the CardBus bridge's IO window.
The default value is 256 bytes. The default value is 256 bytes.