On Thu, Feb 13, 2020 at 12:40:59PM -0500, Sadanand Warrier wrote:
Hi I had question about PCIe hotplug. We have hardware that is connected to the host by means of two PCIe switches. i.e. the host sees a PCIe switch connected to one of its buses and on the far side of that switch another PCIe switch which has a PCIe device. It is possible that this device does not train its host facing PCIe links before the server enumerates down its PCI bus and reaches those links. It is also possible the PCIe switch to which the device is attached has not been able to train its own links before server enumeration. Is PCIe hotplug built to work on schemes like this? Let us assume that the hardware has been designed to trasmit a presence signal once the links are trained but this could happen after the server enumeration?
Look at the PCIe hotplug spec, it should answer all of your questions about this.
Incidentally does the server take advantage of the BIOS/UEFI enumeration?
Yes, of course, how else would the kernel be able to enumerate PCI devices? :) thanks, greg k-h