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SubjectRe: [PATCH] PCI: Document PCIE BUS MPS parameters
On Wed, Jan 23, 2013 at 08:01:36AM +0000, Yijing Wang wrote:
> Document PCIE BUS MPS parameters pcie_bus_tune_off, pcie_bus_safe,
> pcie_bus_peer2peer, pcie_bus_perf into Documentation/kernel-parameters.txt.
> These parameters were introduced by Jon Mason <mason@myri.com> at
> commit 5f39e6705 and commit b03e7495a8. Document these into
> kernel-parameters.txt help users to understand and use the parameters.
>
> Signed-off-by: Yijing Wang <wangyijing@huawei.com>
> ---
> Documentation/kernel-parameters.txt | 13 +++++++++++++
> 1 files changed, 13 insertions(+), 0 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 363e348..4dfa8d2 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2227,6 +2227,19 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> This sorting is done to get a device
> order compatible with older (<= 2.4) kernels.
> nobfsort Don't sort PCI devices into breadth-first order.
> + pcie_bus_tune_off [X86] Disable PCI-E MPS turning and using
> + the BIOS configured MPS defaults.
> + pcie_bus_safe [X86] Use the smallest common denominator MPS
> + of the entire tree below a root complex for every device
> + on that fabric. Can avoid inconsistent mps problem caused
> + by hotplug.
> + pcie_bus_perf [X86] Configure pcie device MPS to the largest
> + allowable MPS based on its parent bus.Improve performance
> + as much as possible.
> + pcie_bus_peer2peer [X86] Make the system wide MPS the smallest
> + possible value (128B).This configuration could prevent it
> + from working by having the MPS on one root port different
> + than the MPS on another.
> cbiosize=nn[KMG] The fixed amount of bus space which is
> reserved for the CardBus bridge's IO window.
> The default value is 256 bytes.
>
I was searching for documentation on this the other day.

It's not just X86 that use these options, PowerPC and Tile also use them (grep
for users of pcie_bus_configure_settings). I've also noticed a call to it from
hotplug as well...

In addition these options also have an effect on MRRS - I've not figured out
what effect they have, but you can look in drivers/pci/probe.c at the
pcie_write_mrrs function.

Andrew Murray



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