On Thu, May 03, 2012 at 10:39:42AM -0600, Bjorn Helgaas wrote: >On Thu, May 3, 2012 at 12:21 AM, Richard Yang ><weiyang@xxxxxxxxxxxxxxxxxx> wrote: >> On Wed, May 02, 2012 at 08:59:40AM -0600, Bjorn Helgaas wrote: >>>On Wed, May 2, 2012 at 12:24 AM, Richard Yang >>><weiyang@xxxxxxxxxxxxxxxxxx> wrote: >>>> On Mon, Apr 30, 2012 at 09:56:13AM -0600, Bjorn Helgaas wrote: >>>>>On Fri, Apr 27, 2012 at 11:01 PM, Richard Yang >>>>><weiyang@xxxxxxxxxxxxxxxxxx> wrote: >>>>> >>>> Thanks for your nice chart. >>>>>I think assignments shown for the PCIe-to-PCI bridge are OK, although >>>>>I would draw it like this because the bridge originates a single bus >>>>>02 that may have multiple devices attached to it (this side is PCI, >>>>>not PCIe, so it really is a shared bus): >>>>> >>>>> ^ >>>>> | >>>>> +--------+--------+ >>>>> | 00:02.0 | >>>>> | PCIe-PCI bridge | >>>>> | | >>>>> +--------+--------+ >>>>> | >>>>> | >>>>> +---------------------+ Bus 02 >>>>> | | >>>>> | | >>>>> | | >>>>> +----v----+ +----v----+ >>>>> | 02:00.0 | | 02:01.0 | >>>>> +---------+ +---------+ >>>>> >>>> So for this case, there is not internal bus, while this is really a >>>> physical shared bus, not a logical one. >>> >>>Yes. The downstream side of the PCIe-PCI bridge is PCI. >>> >>>>>I think the PCIe switch part is incorrect. Here's Figure 1-3 from sec >>>>>1.3.3 of the PCIe r3 spec: >>>> >>>>>A PCIe switch appears as two or more PCI-PCI bridges. One is >>>>>associated with the upstream port; the others with the downstream >>>>>ports. >>>>> >>>>>A bridge always has a primary side and a secondary side. In your >>>>>diagram, the bridge associated with the upstream port would be 00:01.0 >>>>>(primary bus 00) and could have a secondary bus of 03 (since 02 is >>>>>already consumed by the PCIe-PCI bridge). >>>> Hmm... I am confused why is 03. 02 is used but 01 is not used. >>>> Switch should be configured after PCIe2PCI bridge? >>> >>>It's likely that the PCIe switch would be configured first, since its >>>device number is lower, but that is not a requirement. The >>>requirement is that the bus number ranges consumed by bridges be >>>non-overlapping. In this case (using your original topology plus my >>>PCIe switch diagram), we'd have: >>> >>> 1. an endpoint at 00:00.0 -- consumes no additional buses >>> 2. a PCIe switch at 00:01.0 -- consumes at least [bus 03-06] >>> 3. a PCIe-PCI bridge at 00:02.0 -- consumes least [bus 02] (its secondary bus) > >> So this is a sequence issue. Below is also a valid configuration. >> 2. a PCIe switch at 00:01.0 -- consumes at least [bus 02-05] >> 3. a PCIe-PCI bridge at 00:02.0 -- consumes least [bus 06] (its secondary bus) > >Yes, this would also be valid. > >>>Bus 03 is the internal PCIe switch bus that connects the upstream port >>>to the downstream ports. Buses 04, 05, and 06 are the links >>>originating from the downstream ports. >>> >>>>>The bridges associated with the downstream ports are all logically on >>>>>bus 03. Their primary bus number would be 03; they might be 03:00.0, >>>>>03:01.0, 03:02.0, etc. Each would have its own secondary bus number, >>>>>for example 04, 05, 06. That secondary bus number is for the >>>>>downstream link from the corresponding downstream port. >>>> Hmm, as you mentioned in previous letter, PCIe is an point-to-point >>>> protocol, then the secondary bus should reside in the Switch? >>>> Do you think my Bus#4 is correct? >>> >>>No. Bus 04 is a PCIe link that connects the downstream port (03:00.0) >>>to a single PCIe device. That device (04:00) could be a PCIe >>>endpoint, or it could be the upstream port of another PCIe switch. >>>(If it is a switch, more bus numbers would be required.) >> >> >> ^ >> | >> +-------------------------------|------------------------------+ >> | | | >> | +----+----+ | >> | | virtual | | >> | | PCI-PCI | | >> | | bridge | | >> | +----+----+ | >> | | | >> | |Bus#3 | >> | | | >> | +----------------------------------------+ | >> | | | | | >> | | | | | >> | |03:00.0 |03:01.0 |03:02.0 | >> | +----+----+ +----+----+ +----++---+ | >> | | virtual | | virtual | | virtual | | >> | | PCI-PCI | | PCI-PCI | | PCI-PCI | | >> | | bridge | | bridge | | bridge | | >> | +----+----+ +----+----+ +----+----+ | >> | | | | | >> | | | | | >> +----------|--------------------|-------------------|----------+ >> | Bus#4? | | >> v v v >> >> So the link itself is Bus#4? > >Exactly. > >> If there is no device under this link, will Bus#4 appear in kernel? > >Yes, I'm pretty sure we build the bus 04 pci_bus structure, then scan >bus 04 for devices. Even if we find none, the pci_bus struct for bus >04 remains. > >> And then the PCIe switch is represented by 4 pci_dev structure and each >> is bridge type? > >Yes. And each has an associated pci_bus struct for its secondary bus. Bjorn Thanks a lot :) Your patient reply answer my question clearly. Those questions confused me a lot. Now I think I get a more clear view about how pci system is represented in the kernel. Thanks again. > >Bjorn -- Richard Yang Help you, Help me -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
