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Date: Fri, 11 May 2018 21:03:31 +0200 (CEST)
From: Wojciech Puchar <wojtek@puchar.net>
To: Dieter BSD <dieterbsd@gmail.com>
cc: freebsd-hardware@freebsd.org, freebsd-hackers@freebsd.org
Subject: Re: PCIe multipliers, how do they work?
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> There are also PCIe cards which provide multiple slots, typically
> connected with a usb cable.  These tend to convert 1 PCIe_x1 slot
> into multiple PCIe_x1 slots.  I get the impression that these do
> not require bifurcation support.  They seem to be aimed at "miners"

these cards consist of PCIe switch which is supported out of the box.
former ones require BIOS to reconfigure CPUs PCI lanes so instead of eg 
one 16x lane there will be 4 4x lanes.