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Date: Fri, 30 Sep 2011 09:03:24 +0200
Subject: Re: Workaround for Intel MPS errata
From: "Rolf Eike Beer" <eike-kernel@sf-tec.de>
To: "Jon Mason" <mason@myri.com>
Cc: "Avi Kivity" <avi@redhat.com>, "Sven Schnelle" <svens@stackframe.org>,
        "Simon Kirby" <sim@hostway.ca>,
        "Eric Dumazet" <eric.dumazet@gmail.com>,
        "Niels Ole Salscheider" <niels_ole@salscheider-online.de>,
        "Jesse Barnes" <jbarnes@virtuousgeek.org>,
        "Linus Torvalds" <torvalds@linux-foundation.org>,
        "linux-kernel" <linux-kernel@vger.kernel.org>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        "Ben Hutchings" <bhutchings@solarflare.com>
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> Hey Avi,
> Can you try this patch?  It should resolve the issue you are seeing.
>
> Thanks,
> Jon
>
>     PCI: Workaround for Intel MPS errata
>
>     Intel 5000 and 5100 series memory controllers have a known issue if
> read
>     completion coalescing is enabled (the default setting) and the PCI-E
>     Maximum Payload Size is set to 256B.  To work around this issue,
> disable
>     read completion coalescing if the MPS is 256B.
>
>     http://www.intel.com/content/dam/doc/specification-update/5000-chipset-memory-controller-hub-specification-update.pdf
>     http://www.intel.com/content/dam/doc/specification-update/5100-memory-controller-hub-chipset-specification-update.pdf
>
>     Reported-by: Avi Kivity <avi@redhat.com>
>     Signed-off-by: Jon Mason <mason@myri.com>
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index a919db2..13c733a 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1361,6 +1361,80 @@ static int pcie_find_smpss(struct pci_dev *dev,
> void *data)
>  	return 0;
>  }
>
> +static void pcie_errata_check(int mps)
> +{

While this whole function is about Intel 5x00 devices the name of it is
very generic (and in a very generic file). Maybe this can be changed, e.g.
"fixup:" renamed to "fixup_intel_5x00:". Also I wonder if that shouldn't
be a nop when CONFIG_PCI_QUIRKS is not set.

Eike