Re: [PATCH] PCI: update device mps when doing pci hotplug

[Yijing Wang <wangyijing@huawei.com>]

On 2014/9/26 0:46, Keith Busch wrote:
> On Wed, 24 Sep 2014, Yijing Wang wrote:
>> On 2014/9/25 7:30, Bjorn Helgaas wrote:
>>> On Wed, Sep 24, 2014 at 4:41 PM, Keith Busch <keith.busch@intel.com> wrote:
>>>> Just poking this thread to make sure it's not dead. :)
>>>>
>>>> I tested Yijing's proposal and it is successful on our Intel server
>>>> platforms; hoping either this or something that derives similar behavior
>>>> will be applied so we can remove bus tuning kernel parameters.
>>>>
>>>> Tested-by: Keith Busch <keith.busch@intel.com>
>>>
>>> Oops, thanks for poking me, because this was indeed dead.
>>>
>>> My main objection was to testing "is_hotplug_bridge".  That doesn't
>>> seem right, because this issue really isn't specific to hotplug.  I
>>> didn't see a resolution of that, but let me know if I missed it.
>>
>> Why I introduced "is_hotplug_bridge" is to avoid to touch the MPS which is not
>> in hotplug case when pcie_bus_config == PCIE_BUS_TUNE_OFF.
>>
>> It's so sad that PCIe spec doesn't give a detailed guide to configure MPS.
>>
>> I'd like to refactor current MPS framework, but now there are still some puzzles
>> to me. I need to have a deeper understanding of pcie mps. I read Jon's mps patch
>> log from git, I found he turn off all this MPS config, because some issues were found
>> in some platforms, but no platforms detailed info and no bugzilla records.
> 
> Just my opinion, I thought the hotplug check was a good idea: it addresses
> a known issue, and does not mess with current unknowns. Outside a hotplug
> scenario, I think we expect platform f/w to handle MPS settings and the
> kernel can stay out of the way because of the unknown platform issues. If
> it is hotplug, having the kernel set device's MPS to match the parent
> couldn't make things worse off than doing nothing, right?

Yes, I think so, but it all decided by Bjorn. I think he want a better solution,
and current patch just still is a temporary fix.

> 
> On the side, I'll see if I can ping some comrades on PCI-SIG to propose
> an ECN to clarify configuring MPS. They usually ignore me though, so no
> promises. :)

Thanks in advance for your help :)

> 
> .
> 


-- 
Thanks!
Yijing