Re: [dpdk-dev] [PATCH] bus/pci: support segment value as address domain on Windows

["Menon, Ranjit" <ranjit.menon@intel.com>]

On 9/10/2020 12:30 AM, Tal Shnaiderman wrote:
>> Subject: Re: [PATCH] bus/pci: support segment value as address domain on
>> Windows
>>
>> On Tue, Aug 25, 2020 at 02:43:16PM +0300, Tal Shnaiderman wrote:
>>> Set the domain value for rte_pci_addr probing on Windows to the value
>>> of the PCI segment returned by SPDRP_BUSNUMBER.
>>>
>>> Signed-off-by: Tal Shnaiderman <talshn@nvidia.com>
>>> ---
>>>   drivers/bus/pci/windows/pci.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/bus/pci/windows/pci.c
>>> b/drivers/bus/pci/windows/pci.c index 489aa7902a..a40acec609 100644
>>> --- a/drivers/bus/pci/windows/pci.c
>>> +++ b/drivers/bus/pci/windows/pci.c
>>> @@ -195,8 +195,8 @@ get_device_pci_address(HDEVINFO dev_info,
>>>   		return -1;
>>>   	}
>>>
>>> -	addr->domain = 0;
>>> -	addr->bus = bus_num;
>>> +	addr->domain = bus_num >> 8;
>>> +	addr->bus = bus_num & 0xff;
>>>   	addr->devid = dev_and_func >> 16;
>>>   	addr->function = dev_and_func & 0xffff;
>>>   	return 0;
>>> --
>> Is this needed to avoid collision of devices with the same B:D:F?
> Right, it can happen in virtualization setups when several virtual functions can have the same BDF, e.g.:
>
> PS  > Get-NetAdapterHardwareInfo
>
> Name                           Segment Bus Device Function Slot NumaNode PcieLinkSpeed
> ----                           ------- --- ------ -------- ---- -------- -------------
> Ethernet                                   0   0     10       0                      Unknown
> Ethernet 4                       58601   0      2        0             0       Unknown
> Ethernet 5                       52956   0      2        0             0       Unknown
>
> DPDK currently can detect either Ethernet 4 or ethernet 5 if only BDF is checked.
> Unix uses the Domain value, the equivalent value for Windows is Segment.

Thanks for the explanation, Tal.

I had always been curious how Windows stores the PCIe segment (domain) 
number.

On VMs hosted on Hyper-V, the VF segment numbers are always in the high 
16-bit values.

Is this documented somewhere, or did you find this by experimentation?


ranjit m.