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

[Keith Busch <keith.busch@intel.com>]

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>

On Thu, 4 Sep 2014, Yijing Wang wrote:
>>>>>      if (pcie_bus_config == PCIE_BUS_TUNE_OFF) {
>>>>> +            pcie_bus_update_set(dev);
>>>>
>>>> You're only adding this to the PCIE_BUS_TUNE_OFF path.  Can't the same
>>>> problem occur for other pcie_bus_config settings?
>>>
>>> We only found the problem during PCIE_BUS_TUNE_OFF set. Other mode like PCIE_BUS_SAFE and PCIE_BUS_PEER2PEER.
>>> This issue won't happen.
>>
>> Sorry, I can't parse this.  Are you saying the problem won't happen in
>> the other modes?  Why not?
>
> Hi Bjorn, when in PCIE_BUS_SAFE mode, pcie_find_smpss() will find the largest available mpss in a pcie path.
> Then call pcie_bus_configure_set() to set all devices' mps to the largest available mps in this path, so
> all devices in the path will have the same mps. When in PCIE_BUS_PEER2PEER, all devices' mps will be set to 128B
> for safety. And to the PCIE_BUS_PERFORMANCE mode, I found Jon's comment in pcie_write_mps(),
>
> 			/* For "Performance", the assumption is made that
> 			 * downstream communication will never be larger than
> 			 * the MRRS.  So, the MPS only needs to be configured
> 			 * for the upstream communication.  This being the case, <------
> 			 * walk from the top down and set the MPS of the child
> 			 * to that of the parent bus.
>
> So I think the problem won't happen in other modes.
>
> Thanks!
> Yijing.
>
>
>>
>>>>>              pcie_bus_detect_mps(dev);
>>>>>              return 0;
>>>>>      }
>>
>> .
>>
>
>
> -- 
> Thanks!
> Yijing
>
>