Re: Fail to probe qla2xxx fiber channel card while doing pci hotplug

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On Thu, Sep 20, 2012 at 6:26 AM, Yijing Wang <wangyijing@xxxxxxxxxx> wrote:
> On 2012/9/20 9:47, Yijing Wang wrote:
>>>> We compared the two situations after BIOS initialization, and found Max Payload Size in DEVCTRL is 256B
>>>> if FC card had been installed, if the slot is empty, Max Payload Size is 128B. We force it to be 128B when
>>>> FC card installed when system boot up. Finally pci hotplug becomes ok. So I suspect maybe our PCIe hardware
>>>> has problem supporting 256B.
>>>
>>> Ah, this sounds like something I've been worried about for a while,
>>> i.e., do we handle MPS correctly when we hot-add devices?
>>>
>>> Yijing, I'm not quite clear on what you're observing.  I guess you're
>>> saying that if an FC card is installed at boot, the BIOS sets MPS to
>>> 256, and that if no FC card is installed, the BIOS sets MPS to 128?
>>
>> Yes.
>>
>>> You haven't mentioned any Linux boot options, so I assume you haven't
>>> tried any.  Does "pci=pcie_bus_safe" make any difference?
>>
>> Yes, I don't add any Linux boot options before. I will try this boot option
>> "pci=pcie_bus_safe".
>>
>>> Jon, here's a pointer to the beginning of the thread:
>>> http://marc.info/?l=linux-pci&m=134770460302298&w=2 (full dmesg log at
>>> http://marc.info/?l=linux-scsi&m=134788365823217&w=2).  I'm not sure
>>> we have enough in the dmesg log to diagnose an issue like this.  I
>>> wonder if it would be useful to log the current setting, so we could
>>> notice BIOS default differences like this one.
>>>
>
> Hi Bjorn,
>    After add "pci=pcie_bus_safe" boot options, Hot-plug for FC card is OK.
> It's great! Thanks for your help!
>
> Giri, it's not the fc card problem, we fix this problem by add boot option
> "pci=pcie_bus_safe" which force the MPS of the entire system to the smallest
> possible.

That's OK for a workaround, but it'd definitely not a complete
solution.  At the very least, we need some kind of info in dmesg that
will enable us to diagnose the problem next time somebody runs into
it.  *You* are sophisticated enough to poke around and look at MPS
settings manually, but the next person who runs into it will not be.
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