USB 3.2 Gen 2x2 "Superspeed+20GBps" support for ASM3242

[William Allen <william.allentx@gmail.com>]

I've never submitted to the mailing list before, so please excuse any
formalities that I may not be observing.
I would like to be able to use USB 3.2 Gen2x2 "SuperSpeed+²⁰Gbps"
under Linux. I've tried several different kernel versions, and have
built the kernel from the usb-next tree. All without finding proper
functionality.

I have an Ableconn PEX-UB159 USB 3.2 Gen 2x2 PCIe expansion card, with
the ASM3242 controller. This controller appears to be the only Gen2x2
capable controller that exists in commercial products- so far as I've
found. Everything appears to work, except for "SuperSpeed+²⁰Gbps" when
I plug in a capable device.
Here is the dmesg output as soon as I plug in a Gen2x2 WD P50 Black
External NVMe SSD, using an appropriate SuperSpeed+²⁰Gbps certified
cable:
5.11.2-arch1-1
--------------------
usb 7-2: new SuperSpeedPlus Gen 2 USB device number 3 using xhci_hcd
usb 7-2: New USB device found, idVendor=1058, idProduct=2642, bcdDevice=10.03
usb 7-2: New USB device strings: Mfr=2, Product=3, SerialNumber=1
usb 7-2: Product: Game Drive
usb 7-2: Manufacturer: Western Digital
usb 7-2: SerialNumber: 323130334431343030303736
scsi host11: uas
scsi 11:0:0:0: Direct-Access     WD       Game Drive       1003 PQ: 0 ANSI: 6
scsi 11:0:0:1: Enclosure         WD       SES Device       1003 PQ: 0 ANSI: 6
sd 11:0:0:0: [sdf] 3907029168 512-byte logical blocks: (2.00 TB/1.82 TiB)
sd 11:0:0:0: [sdf] Write Protect is off
sd 11:0:0:0: [sdf] Mode Sense: 57 00 10 00
sd 11:0:0:0: [sdf] Write cache: enabled, read cache: enabled, supports
DPO and FUA
sd 11:0:0:0: [sdf] Optimal transfer size 33553920 bytes
sd 11:0:0:0: [sdf] Attached SCSI disk

 When I saw commits referring to Gen2x2 in the usb-next repo, I built
off that, and also ran linux-next-git.r0.gabaf6f60176f-1 from AUR,
both giving me the same results/output:
linux-next-git.r0.gabaf6f60176f-1
----------------------------------------------
usb 5-1: new SuperSpeed Gen 1x2 USB device number 3 using xhci_hcd
usb 5-1: New USB device found, idVendor=1058, idProduct=2642, bcdDevice=10.03
usb 5-1: New USB device strings: Mfr=2, Product=3, SerialNumber=1
usb 5-1: Product: Game Drive
usb 5-1: Manufacturer: Western Digital
usb 5-1: SerialNumber: 323130334431343030303736
scsi host7: uas
scsi 7:0:0:0: Direct-Access     WD       Game Drive       1003 PQ: 0 ANSI: 6
scsi 7:0:0:1: Enclosure         WD       SES Device       1003 PQ: 0 ANSI: 6
ses 7:0:0:1: Attached Enclosure device
ses 7:0:0:1: Failed to get diagnostic page 0x1
ses 7:0:0:1: Failed to bind enclosure -19
sd 7:0:0:0: [sdf] 3907029168 512-byte logical blocks: (2.00 TB/1.82 TiB)
sd 7:0:0:0: [sdf] Write Protect is off
sd 7:0:0:0: [sdf] Mode Sense: 57 00 10 00
sd 7:0:0:0: [sdf] Write cache: enabled, read cache: enabled, supports
DPO and FUA
sd 7:0:0:0: [sdf] Optimal transfer size 33553920 bytes
sd 7:0:0:0: [sdf] Attached SCSI disk

See that it's detecting it as Gen 1x2.
The output of lsusb -t shows that it is connected at 5000M using the
uas driver. Even my much slower USB 3.1 SSDs connect at 10000M on the
exact same port.
When I attach the Gen2x2 NVMe SSD to my other 3.2 Gen2 card, it
connects at 10000M, so It seems to be directly related to a
mishandling when the Gen2x2 device gets recognized by the Gen2x2 card.

lspci output from 5.11.2-arch1-1:
-------------------------------------------
USB controller: ASMedia Technology Inc. ASM3242 USB 3.2 Host
Controller (prog-if 30 [XHCI])
Subsystem: ASMedia Technology Inc. ASM3242 USB 3.2 Host Controller
Physical Slot: 1
Flags: bus master, fast devsel, latency 0, IRQ 62, NUMA node 0
Memory at f7df0000 (64-bit, non-prefetchable) [size=32K]
Capabilities: [50] MSI: Enable- Count=1/8 Maskable- 64bit+
Capabilities: [68] MSI-X: Enable+ Count=8 Masked-
Capabilities: [78] Power Management version 3
Capabilities: [80] Express Legacy Endpoint, MSI 00
Capabilities: [c0] Subsystem: ASMedia Technology Inc. Device 0201
Capabilities: [100] Advanced Error Reporting
Capabilities: [200] Secondary PCI Express
Capabilities: [300] Latency Tolerance Reporting
Capabilities: [400] L1 PM Substates
Kernel driver in use: xhci_hcd
Kernel modules: xhci_pci

I'm happy to test anything, or file this somewhere more appropriate if
you could point me in the right direction.