Just to point-out that pictures in §19.2 PCIe chapter in i.MX 8DualX/8DualXPlus/8QuadXPlus Reference Manual (IMX8DQXPRM) - Rev 0, 05/2020 cannot be read as they are pictures rather than vector images. Example which can't be read at all, even when zooming:
Figure 19-12. Controller Configuration Space Layout: (RC Mode)
Figure 19-14. AXI ATS Sideband Signal Usage
Figure 19-30. Linked List Flow for Producer and Consumer
Also, in general, the chapter is not well presented: a lot of text duplication, multiple figures without figure number, very limited explanation in registers (e.g. PF0_PORT_LOGIC), etc. Needs a peer review...
I don't know if the forum is the good place to report documentary issues, but please update the Reference Manual with better quality images (raster/vector searcheable images would be preferable by the way).