SD Card Reader Not Detected on Lenovo P16 Gen 2 - Realtek rtsx Device Enters D3hot

[CaelumofAethryn]

Hardware:

Lenovo ThinkPad P16 Gen 2 (21FA0027US)
SD Card Reader: Realtek Semiconductor Device [10ec:5261]

Kernel Versions Affected:

6.12
6.16
6.17.9-76061709-generic

Symptoms:
SD card reader does not detect card insertion. Device automatically enters D3hot (low power state) and fails to wake when card is inserted.
Root Cause Identified:
The PCIe Root Port (0000:00:1c.4) suspends due to aggressive runtime power management. When the root port suspends, the rtsx device loses wake signal capability and card insertion interrupts never reach the kernel.
Workaround:
Forcing the root port to D0 (full power) restores functionality:

Lenovo P16 Gen 2 SD Card Reader Bug Report.pdf

[7thgentreeservice-a11y]

Verified Workaround

The following udev rule resolves the issue by keeping both the PCIe Root Port and rtsx device in D0 (full power):

Create /etc/udev/rules.d/99-rtsx-wakeup.rules with:

SUBSYSTEM=="pci", ATTR{vendor}=="0x8086", ATTR{device}=="0x7a3c", RUN="/bin/sh -c 'echo on > /sys/$devpath/power/control'"
SUBSYSTEM=="pci", ATTR{vendor}=="0x10ec", ATTR{device}=="0x5261", RUN="/bin/sh -c 'echo on > /sys/$devpath/power/control'"

Then reload udev:
bashsudo udevadm control --reload
sudo udevadm trigger
sudo reboot

After this, SD card detection works immediately upon insertion. This confirms the issue is runtime power management preventing wake signals from reaching the device.