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

[Ping-Ke Shih <pkshih@realtek.com>]

LB F <goainwo@gmail.com> wrote:
> Ping-Ke Shih <pkshih@realtek.com> wrote:
> > I add a printk to show the case VHT and NSS==0 as below. Please help to
> > collect the output, and then I can see what it happened.
> 
> Hi Ping-Ke,
> 
> I applied your diagnostic patch (using pr_err for maximum log
> visibility) and spent the last couple of days testing it on the
> affected hardware. The results answer both open questions cleanly.
> 
> ---
> 
> Regarding your earlier question:
> > Not sure if this is because PCIE bridge has no ASPM capability?
> 
> You were correct. The very beginning of the boot log shows:
> 
>   [0.177872] ACPI FADT declares the system doesn't support PCIe ASPM,
>               so disable it
>   [15.157752] r8169 0000:07:00.0: can't disable ASPM; OS doesn't have
>                ASPM control
> 
> The BIOS on this HP laptop uses the ACPI FADT table to globally revoke
> OS control over PCIe ASPM before Linux even takes over. This has an
> important implication: since ASPM is already disabled at the hardware
> level by firmware, the instability on this specific SKU is caused
> entirely by LPS Deep Mode, not ASPM itself.

Checking rtw88 code related to rtw_pci_disable_aspm, I found that driver
does check device ASPM capability before configuring ASPM. It looks 
a little weird why OS doesn't turn off these capabilities of device.
Maybe we should check the capabilities of PCI bridge side? 

> 
> This explains why the ASPM-only quirk (v1 patch) did not stop the h2c
> timeouts -- ASPM was never actually active on this machine to begin
> with. Disabling LPS Deep Mode via the v2 quirk is what eliminates the
> firmware timeout loop entirely.

I think there are two problems. One is ASPM causing system frozen, and
the other is LPS deep mode causing H2C timeouts. If you turn on ASPM
and disable LPS deep mode, I feel H2C timeout can disappear, but it
might go frozen first though. 

Ping-Ke