On Thu, Feb 11, 2016 at 05:22:15PM +0200, Ran Shalit wrote: > If I may please ask one more on this issue. > You have made it clear the terms lanes & device in relation to > PCI/PCI-e device driver. > What about port ? Is there any relation between port to lane/device or > is there no relation between these terms. In Linux, PCIe Ports (Root Ports, Switch Upstream Ports, or Switch Downstream Ports) are treated as devices. There is a struct pci_dev for each Port. A Switch contains at least two Ports (an Upstream Port and one or more Downstream Ports), and there is a pci_dev for each of them. There is no connection between the number of lanes and the number of pci_dev structs. The Linux PCI core doesn't do anything with the number of lanes. My understanding is that the devices on either end of a Link normally negotiate the link width (number of lanes) between themselves automatically, without software intervention. > For example, can it be 1 device with 2 lanes and 8 ports for example ? "1 device with 8 ports" is a phrase that would make sense in the PCIe spec, where you could be talking about a Switch with one Upstream Port and seven Downstream Ports. But in the Linux kernel, since we treat each PCI/PCIe *function* as an independent device, this looks like 8 devices. There will be 8 pci_dev structs, one for each port. The "2 lanes" part is irrelevant. The number of lanes makes no difference as far as how many pci_dev structs we have. Bjorn -- 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
