On Mon, Feb 1, 2016 at 10:54 PM, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > On Mon, Feb 01, 2016 at 08:41:28PM +0200, Ran Shalit wrote: >> On Mon, Feb 1, 2016 at 6:14 AM, Alex Williamson >> <alex.williamson@xxxxxxxxxx> wrote: >> > On Sun, 2016-01-31 at 02:15 -0500, Ran Shalit wrote: >> >> Hello, >> >> >> >> I am new to pci express drivers, and would please like to ask a question. >> >> We develop a linux driver for a PCIe device board with 4 lanes. >> >> 1. Is it expected that this will be recognized as a single device or >> >> multiple device ? >> > >> > It depends whether your device is multifunction. >> >> It is a video capture & output deivce, (video4linux), so I guess it >> means it has single functionality (video).' and therefore will aprear >> as a single device. > > I'm not familiar with video devices, but it sounds likely that there > would be at least two functions (one for input, another for output). > > It's a little confusing because the PCI/PCIe specs use "bus", > "device", and "function" to describe device addressing, but in the > Linux kernel, when we talk about a PCI device, we mean an individual > *function*. We maintain a struct pci_dev for each function, and a > driver binds to the pci_dev for a single function. > > If you run "lspci", it shows a line for each function. Here are a few > from my system: > > 00:1b.0 Audio device: Intel Corporation Lynx Point-LP HD Audio Controller > 00:1c.0 PCI bridge: Intel Corporation Lynx Point-LP PCI Express Root Port 1 > 00:1c.3 PCI bridge: Intel Corporation Lynx Point-LP PCI Express Root Port 4 > 00:1c.5 PCI bridge: Intel Corporation Lynx Point-LP PCI Express Root Port 6 > > The 00 is the PCI bus number; 1b and 1c are PCI device numbers; the > .0, .3, and .5 are PCI function numbers. In PCI spec terms, this is > one single-function device (the audio controller at 00:1b.0) and one > multi-function device with three functions (the root ports at 00:1c). > > In the kernel, we manage each function individually, so there are four > pci_dev structs for the above list, and there could be four separate > drivers bound to them. > >> >> 2. Is it that each lane rales to a different BAR or there is no >> >> connection between these two ? >> > >> > No relation, all PCI/e devices have the same set of standard BARs >> > available to them. >> >> So it probably means that there is no added complexity in terms of >> device driver with multi lanes PCIe (compared to single lane). > > Right. The number of PCIe lanes is invisible to the driver. There > are ways to find out and influence how many lanes a device uses, but > in general, there's no need to do that. > > Bjorn Hello, 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. For example, can it be 1 device with 2 lanes and 8 ports for example ? Thank you very much, Ran -- 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
