linux-kernel - Re: [PATCH 1/1] ia64/pci: set mmio decoding on for some host bridge

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Date:	Tue, 9 Jul 2013 10:49:49 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	"Li, Zhen-Hua" <zhen-hual@...com>
Cc:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] ia64/pci: set mmio decoding on for some host bridge

On Mon, Jul 8, 2013 at 11:42 PM, Li, Zhen-Hua <zhen-hual@...com> wrote:
> On some IA64 platforms with intel PCI bridge, for example, HP BL890c i2
> with  Intel Corporation 5520/5500/X58 I/O Hub PCI Express Root Port,
> when kernel tries to disable the mmio decoding on the PCI bridge devices,
> kernel may crash.
>
> And in the comment of function quirk_mmio_always_on, it also says:
> "But doing so (disable the mmio decoding) may cause problems on host bridge
>  and perhaps other key system devices"
>
> So, for this PCI bridge,  dev->mmio_always_on bit should be set to 1.
>
> To avoid affecting the use of quirk_mmio_always_on, a new function is created.
>
> Signed-off-by: Li, Zhen-Hua <zhen-hual@...com>
> ---
>  drivers/pci/quirks.c    |   17 +++++++++++++++++
>  include/linux/pci_ids.h |    1 +
>  2 files changed, 18 insertions(+)
>
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index e85d230..665af3e 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -44,6 +44,23 @@ static void quirk_mmio_always_on(struct pci_dev *dev)
>  DECLARE_PCI_FIXUP_CLASS_EARLY(PCI_ANY_ID, PCI_ANY_ID,
>                                 PCI_CLASS_BRIDGE_HOST, 8, quirk_mmio_always_on);
>
> +#ifdef CONFIG_IA64
> +/*
> + * On some IA64 platforms, for some intel PCI bridge devices, for example,
> + * the Intel Corporation 5520/5500/X58 I/O Hub PCI Express Root Port,
> + * disable the mmio decoding on this device may cause system crash.
> + * So dev->mmio_always_on bit should be set to 1.
> + */
> +static void quirk_mmio_on_intel_pcibridge(struct pci_dev *dev)
> +{
> +       dev->mmio_always_on = 1;
> +}
> +DECLARE_PCI_FIXUP_CLASS_EARLY(PCI_VENDOR_ID_INTEL,
> +                       PCI_DEVICE_ID_INTEL_5520_5550_X58,
> +                       PCI_CLASS_BRIDGE_PCI,
> +                       8, quirk_mmio_on_intel_pcibridge);
> +#endif
> +
>  /* The Mellanox Tavor device gives false positive parity errors
>   * Mark this device with a broken_parity_status, to allow
>   * PCI scanning code to "skip" this now blacklisted device.
> diff --git a/include/linux/pci_ids.h b/include/linux/pci_ids.h
> index 3bed2e8..d8c60b7 100644
> --- a/include/linux/pci_ids.h
> +++ b/include/linux/pci_ids.h
> @@ -2742,6 +2742,7 @@
>  #define PCI_DEVICE_ID_INTEL_LYNNFIELD_MC_CH2_RANK_REV2  0x2db2
>  #define PCI_DEVICE_ID_INTEL_LYNNFIELD_MC_CH2_TC_REV2    0x2db3
>  #define PCI_DEVICE_ID_INTEL_82855PM_HB 0x3340
> +#define PCI_DEVICE_ID_INTEL_5520_5550_X58       0x3408
>  #define PCI_DEVICE_ID_INTEL_IOAT_TBG4  0x3429
>  #define PCI_DEVICE_ID_INTEL_IOAT_TBG5  0x342a
>  #define PCI_DEVICE_ID_INTEL_IOAT_TBG6  0x342b
> --
> 1.7.10.4
>

You need to figure out what the problem is, not just avoid it.  It's
very unlikely that the problem is something unique to ia64.  In fact,
I think it's very doubtful that the problem is even something unique
to the 5520 root ports.  My guess is there's something special about
the system you're testing.

Evidently you have traffic going to a device behind the root port at
the same time as we're trying to read the root port's BARs.  Linux
should not generate traffic like that while we're enumerating the root
port.  Does the problem happen on a root port with an iLO behind it?
Can you collect "lspci -vvv" output and identify the root port where
the problem occurs?

Bjorn
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