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Linux kernel 2.6
I’ve got an fpga that is loaded over GPIO connected to a development board running linux.
The fpga will transmit and receive data over the pci-express bus. However, this is enumerated
at boot and as such, no link is discovered (because the fpga is not loaded at boot).
How can I force re-enumeration of the pci-e bus in linux?
Is there a simple command or will I have to make kernel changes?
I need the capability to hotplug pcie devices.
I wonder what platform you are on: A work around (aka hack) for this that works on x86 systems is to have the BIOS basically statically configure a PCI device at whatever bus, device, function the FPGA normally lands on, then the OS will enumerate the device and reserve the PCI space for it (even though the device isn’t really there). Then in your device driver you will have to do some extra things like setup the BARs and int lines manually after the fpga has been programmed. Of course this requires modifying the BIOS, which if you are working with a BIOS vendor you can contract them to make this change for you, if you are not working with a BIOS vendor then it will be much harder… Also keep in mind that I was working on VxWorks on x86, and we had a AMI make a custom BIOS for our boards…
If you don’t have a BIOS, then consider programming it in the bootloader, there you already have the ability to read from disk, and adding GPIO capabilities probably isn’t too difficult (assuming you are using jtag and GPIOs?), in fact depending on what bootloader you use it might already be able to do GPIO?
The issues with modifying the kernel to do this is that you have to find the sweet spot where you can read the bitfile, before the PCI enumeration… If for example the disk device drivers are initialized after PCI, then obviously you must do some radical changes to the kernel just to read the bitfile prior to PCI enumeration, which might cause other annoying problems…
One other option which you may have already discovered, and which is really only ok for development time: Power up the system, program the fpga board, then do a reset (without power cycle, for example: sudo reboot now), the FPGA should keep its configuration, and linux should enumerate it…