linux-kernel - Re: [PATCH v3] PCI: Document PCIE BUS MPS parameters

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Message-ID: <CAPoiz9zw-pVNGZC7Ox+Kf+=RNHJRCY5hoLejbrmWmjvHtUEihg@mail.gmail.com>
Date:	Mon, 28 Jan 2013 22:00:37 -0700
From:	Jon Mason <jdmason@...zu.us>
To:	Yijing Wang <wangyijing@...wei.com>
Cc:	Rob Landley <rob@...dley.net>, Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, Andrew Murray <andrew.murray@....com>,
	Joe Lawrence <Joe.Lawrence@...atus.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Hanjun Guo <guohanjun@...wei.com>, jiang.liu@...wei.com
Subject: Re: [PATCH v3] PCI: Document PCIE BUS MPS parameters

On Fri, Jan 25, 2013 at 2:36 AM, Yijing Wang <wangyijing@...wei.com> wrote:
> v0->v1: Update MPS parameters as non-arch and add MRRS
>                 description into pcie_bus_perf parameter suggested
>                 by Andrew Murray.
> v1->v2: Update some semantic problems and add MPS and MRRS
>                 explanation suggested by Joe Lawrence and Randy Dunlap.
> v2->v3: Update some semantic problems and the description
>                 of pcie_bus_safe and pcie_bus_peer2peer suggested
>                 by Bjorn Helgaas.
>
> 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@...i.com> at
> commit 5f39e6705 and commit b03e7495a8.
>
> Signed-off-by: Yijing Wang <wangyijing@...wei.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..2997df2 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       Disable PCIe MPS (Max Payload Size)
> +                               tuning and use the BIOS-configured MPS defaults.
> +               pcie_bus_safe   Use the smallest supported MPS of any device
> +                               below a root complex.

This isn't correct.  It should be something like "The largest MPS
common to all devices below the root complex".

> +               pcie_bus_perf   Configure 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.
>                 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.
> --
> 1.7.1
>
>
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