Re: [BUG] wifi: rtw88: Hard system freeze on RTL8821CE when power_save is enabled (LPS/ASPM conflict)

[LB F]

Ping-Ke Shih <pkshih@xxxxxxxxxxx> wrote:
> Maybe we should check the capabilities of PCI bridge side?
> I think there are two problems. One is ASPM causing system frozen,
> and the other is LPS deep mode causing H2C timeouts.

Hi Ping-Ke,

You were right on both counts. Here are the PCI bridge capabilities.

The upstream bridge for the RTL8821CE (13:00.0) is:
  Intel Corporation Wildcat Point-LP PCI Express Root Port #5 (00:1c.4)

Bridge (00:1c.4):
  LnkCap: Port #5, Speed 5GT/s, Width x1, ASPM L0s L1,
          Exit Latency L0s <512ns, L1 <16us
  LnkCtl: ASPM L0s L1 Enabled

WiFi card (13:00.0):
  LnkCap: Port #0, Speed 2.5GT/s, Width x1, ASPM L0s L1,
          Exit Latency L0s <2us, L1 <64us
  LnkCtl: ASPM L0s L1 Enabled

So ASPM L0s and L1 are enabled by the BIOS on both ends of the bus,
despite the ACPI FADT claiming the OS has no ASPM control. ASPM was
active on this machine all along. I apologize for the incorrect
earlier conclusion that ASPM was not active.

This confirms your analysis: there are indeed two separate problems --
ASPM causing the hard freeze, and LPS Deep Mode causing the H2C
timeouts. The v2 patch correctly addresses both.

---

Regarding your rate validation patch: I applied it (removing the
earlier pr_err block and inserting the new check in
rtw_rx_query_rx_desc). The patch compiled and installed correctly --
verified via strings on the installed .zst module.

I was unable to reproduce the "weird rate" condition or the WARNING
during this test session. The diagnostic module remains installed and
active -- I will report back immediately if I manage to catch it.

Best regards,
Oleksandr Havrylov