What register does PEG Force X1 touch?

[Spoonerd]

A number of Intel chipsets apparently have a setting to force PCIe x1 width. For example, the 3000 chipset datasheet has a remark:

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When Force x1 mode is enabled on this PCI Express link device, this field reflects x1 (01h).

But there is no documentation on how to set this force x1 mode.

Some Asus, etc. BIOS have this setting in their menus as “PEG Force X1”. Does anyone know what register is set for this option?

My endgame is to hack the Dell SC440’s BIOS to not set this force mode.