On Tue, Jun 26, 2012 at 06:16:08AM -0600, Bjorn Helgaas wrote: >On Mon, Jun 25, 2012 at 7:57 PM, Richard Yang ><weiyang@xxxxxxxxxxxxxxxxxx> wrote: >> On Wed, Jun 20, 2012 at 04:45:15PM +0800, Richard Yang wrote: >>>All, >>> >>>I want to confirm something for the pci_dev->resource[]. >>> >>>As in the definition in the pci.h, this resource array is divided into >>>several parts. >>> 0-5 for standard PCI resources >>> 6 for ROM resource >>> 7-10 for bridge resource( if no iov ) >>> >>> >>>1. For P2P bridge, 0-5 is left empty? >>>2. If so, in code pci_setup_device(), I think it set the wrong resource. >>> It call pci_read_bases(dev, 2, PCI_ROM_ADDRESS1), for a p2p bridge. >>> And in pci_read_bases(), BAR information is retrieved and set to >>> pci_dev->resource[0|1]. >>>3. If pci_setup_device() just set first two resource, the child bus will >>> point to empty resource. >>> In pci_alloc_child_bus(), child->resource[0-3] will be point to >>> bridge->resource[7-10], which is not set in pci_setup_device(). >>>4. Another question is, is there any convention for pci_bus->resource[]. >>> [0] for io, [1] for mem, [2] for prefetch? >> All, >> >> I go through the code again and find pci_dev->resource[7-10] is used for >> io/mem base/limit, which is used by the bridge to determine whether it >> will forward one pci transaction. >> >> So pci_dev->[0-1] is used by the bridge's driver? > >Per the PCI-to-PCI Bridge spec v1.2, config space for type 1 devices >(bridges) has two BARs in addition to the I/O, mem, and prefetchable >mem windows. These two BARs are optional and can be used for >device-specific configuration of the bridge itself. This is unrelated >to forwarding transactions. See sec 3.2.5.1. > >The bridge consumes the address space described by the windows and >forwards it to its secondary interface. It also consumes the address >space described by those BARs, without forwarding it. Therefore, we >have to read the BARs to make sure we don't allocate that space to >anything else. > >There *could* be device-specific bridge drivers that actually do >something with those BARs, but I'm not aware of any in Linux. Thanks for your confirmation. :-) > >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
