答复: PCI bus do 2 Enumeration when 2 root bridges under 1 host bridge

[Eric Song <EricSong@zhaoxin.com>]

Hi, Ray
        Thank you very much for explanations.
        I agree with your summary, and I also have tested it.
        But I can't found Pci Io handle is created when a light enumeration.
        So the sequence is as follows:
        1) 1st root bridge handler will trigger Pci bus start() and do enumeration,
        PciEnumerator()->CreateRootBridge() and PciRootBridgeEnumerator , In CreateRootBridge(),it will initialize the PCI I/O instance structure for 1st root bridge.
                 -> CreateRootBridge() and PciRootBridgeEnumerator , In CreateRootBridge(),it will initialize the PCI I/O instance structure for 2rd root bridge.
    2) 2nd root bridge handler will trigger Pci bus start() and do enumeration,
        PciEnumerator()->PciEnumeratorLight().

        So, while 1), all things is done for 2 root bridges. And not populate PciIo for 2nd root bridge.
        Indeed, resource will be allocated based on the host bridge, so notify phase will do all root bridges allocation under host bridge.

Thanks
Eric


-----邮件原件-----
发件人: Ni, Ruiyu [mailto:ruiyu.ni@intel.com]
发送时间: 2017年8月17日 17:59
收件人: Eric Song; edk2-devel@lists.01.org
抄送: Tiger Liu
主题: RE: [edk2] [EDK2] PCI bus do 2 Enumeration when 2 root bridges under 1 host bridge

Eric,
Firstly, PciBus driver can support single-segment-multiple-rootbridge system or multiple-segment-multiple-rootbridge very well. (I agree the enumeration logic confuses you.)

Take a platform containing 2 root bridges for example, your understanding is correct. PciBus does the full enumeration (full means resource assignment is
done) for both root bridges.
But since PciBus driver is a driver model driver and it starts on a root bridge handle, so only the PciIo handles behind that root bridge is created.
The PciIo handles behind the other root bridge is not created until someone starts PciBus again using the other root bridge handle. And when this happens, only a light enumeration happens. Light means bus driver doesn't do the resource assignment but only populate the PciIo.

I guess the full enumeration + light enumeration confuses you.

You may have a question to ask: why not PciBus only does full enumeration on the specified root bridge passed into Start()? Instead of on all root bridges.

My understanding is it's a limitation of the PciHostBridge->NotifyPhase() defined in PI spec.
typedef
EFI_STATUS
(EFIAPI
*EFI_PCI_HOST_BRIDGE_RESOURCE_ALLOCATION_PROTOCOL_NOTIFY_PHASE)
(
IN EFI_PCI_HOST_BRIDGE_RESOURCE_ALLOCATION_PROTOCOL *This, IN EFI_PCI_HOST_BRIDGE_RESOURCE_ALLOCATION_PHASE Phase );

You can see that this interface doesn't carry the RootBridgeHandle so it implies that all root bridges should transfer the state to the next at the same moment.

That's why when even only one root bridge is asked to start, bus driver assigns resources for all root bridges.


In summary, we do have verified the code in single-segment-multiple-rootbridge system and multiple-segment-multiple-rootbridge system.

The driver should work as expected.

Thanks/Ray

> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of
> Eric Song
> Sent: Thursday, August 17, 2017 12:50 PM
> To: edk2-devel@lists.01.org
> Cc: Tiger Liu <TigerLiu@zhaoxin.com>
> Subject: [edk2] [EDK2] PCI bus do 2 Enumeration when 2 root bridges
> under
> 1 host bridge
>
> Hi, experts
>          If there is 2 root bridges under 1 host bridge on the PCI
> hierarchy, whether EDK2 Pci bus driver can support it ? the answer is
> YES, but some confused things in it.
>
> 1)       On BDS phase, ConnectController is called for every root bridge, so Pci
> bus start() will be called for every root bridge.
>
>   VisitAllInstancesOfProtocol (&gEfiPciRootBridgeIoProtocolGuid,
> ConnectRootBridge, NULL);
>
> 2)       In PCI bus driver, Pci start() will do enumeration on the entire host
> bridge
>
> PciEnumerator()->PciHostBridgeEnumerator->”PciResAlloc-
> >GetNextRootBridge()”
>
> That means Do enumeration on entire host bridge for every one root bridge.
> So there are 2 enumerations on entire host bridge for my PCI hierarchy.
>          What I confused is why do 2 enumerations on entire host
> bridge by every one root bridge. Since BDS connect controller by one
> root bridge , Pci bus driver should enumerate corresponding root
> bridge, But it do the entire host bridge which is the parent of the root bridge.
> Or BDS should connect controller by one host bridge, then it will
> match the pci bus driver ‘s enumeration policy.
> In a word, I think it is illogical for current EDKII code.
>
>          Well, the current code execution will do 2 enumerations on
> host bridge for 2 root bridges under 1 host bridge. Even though 2rd
> enumeration would be not full enumeration, but do
> PciEnumeratorLight(), I think it is still not necessary. Whether there
> is any side effect ?  In another word, current PCI bus driver
> enumeration can’t be Suitable for 2 root bridges under 1 host bridge
> or not? It indeed match the PCI hierarchy of 2 host bridges and 1 root bridge under 1 host bridge.
>
> Thanks
> Eric
>
>
>
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