Update: My PCIe works on mainline 5.8.5, worth a try for your PCIe device.
Details here: https://friendlyarm.com/Forum/viewtopic.php?f=61&t=3246

Update: This PCIe M.2 to SATA board works in mainline kernel 5.8.5. $ uname -a Linux hume 5.8.5-g9ece50d8a470-dirty #5 SMP Sat Aug 29 12:18:03 EDT 2020 aarch64 GNU/Linux $ lspci 00:00.0 PCI bridge: Fuzhou Rockchip Electronics Co., Ltd RK3399 PCI Express Root Port 01:00.0 SATA controller: ASMedia Tec...

NanoPC-T4 not detecting M.2 PCIe-SATA card at all. Card: M.2 B+M Key 22x42 PCIe To 2 Port SATA III RAID Adapter Card - SI-ADA40126 https://www.sybausa.com/index.php?route=product/product&product_id=970&search=sata&page=2 Chipset ASMedia 106x https://www.asmedia.com.tw/eng/e_show_products...

Bump. I am getting exactly the same error in kernel log with a M.2 PCIe -> SATA card ASMedia AS106x. https://www.asmedia.com.tw/eng/e_show_products.php?item=151&cate_index=166 https://www.sybausa.com/index.php?route=product/product&product_id=970&search=sata&page=2 The kernel has SAT...