rtw88: The debugfs interface reads registers from the wrong device

Bitterblue Smith <rtl8821cerfe2@xxxxxxxxx> · Mon, 15 Jul 2024 14:05:03 +0300

Hi,

To reproduce the problem, you need a computer with two wifi
devices supported by rtw88. It's especially easy to notice
the problem if one of the devices is USB and the other is PCI,
because the PCI device will have various values in the
registers 0x300..0x3ff, but the USB device will have all
0xeaeaeaea there.

1. Let's assume the driver for the PCI device is already loaded.
   I have RTL8822CE.

2. Mount debugfs:

   # mount -t debugfs none /sys/kernel/debug

3. Check page 0x300:

   # cat /sys/kernel/debug/ieee80211/phy0/rtw88/mac_3
     00000300  f7138000    33330000    ffffb000    00000000
     .....

4. Plug the USB device. I used RTL8811CU.

5. Check page 0x300 again:

   # cat /sys/kernel/debug/ieee80211/phy0/rtw88/mac_3
     00000300  eaeaeaea    eaeaeaea    eaeaeaea    eaeaeaea
     .....

6. Bonus: unload rtw88_8821cu and check page 0x300 again to get
   a null pointer dereference:

   # rmmod rtw88_8821cu
   # cat /sys/kernel/debug/ieee80211/phy0/rtw88/mac_3