Re: [PATCH rtw-next] wifi: rtw88: 8821c: disable deep LPS on PCIe devices

[Bitterblue Smith]

On 19/09/2026 02:28, Paolo Lazzaroni wrote:
> On RTL8821CE PCIe adapters, entering 32kHz low-power clock deep sleep
> (LPS_DEEP_MODE_LCLK) causes recurrent PCIe completion timeouts,
> "firmware failed to leave lps state", "failed to send h2c command",
> and hard system freezes when transitioning out of low power states with
> PCIe ASPM enabled.
> 
> To work around this, a DMI quirk list (rtw_pci_quirks[]) was introduced
> and has grown across HP, ASUS, Dell, and Lenovo machines. However, DMI
> matching is unsustainable: minor sub-model variances (such as ASUS
> FA506II vs FA506IH) or unlisted models (such as ASUS VivoBook X515JA,
> Bmax Y14, or modern Alder Lake-N mini PCs) leave users experiencing bus
> lockups or firmware drops unless they manually turn off power saving via
> iw.
> 
> Examination of official OEM Windows driver INF files for RTL8821CE
> (HP and ASUS netrtwlane.inf) reveals that vendor drivers explicitly
> disable deep power saving (WoWLANPSMode = 0, bLPS_PG_En = 0) and enable

Disabling LPS_PG doesn't mean disabling LCLK, I think.

> firmware PCIe recovery, while keeping standard PCIe ASPM enabled.
> Furthermore, other chips in rtw88 (RTL8723DE, RTL8812AE, RTL8821AE)
> already set lps_deep_mode_supported = 0 by default.

What those other chips are doing is not relevant. RTL8812AE and
RTL8821AE are not officially supported in rtw88. (Not yet?)
lps_deep_mode_supported is zero in rtw8812a.c and rtw8821a.c because
rtw88_usb doesn't implement deep PS and I didn't research which
modes they could support if deep PS was implemented for USB.

> 
> Conservatively disable LPS_DEEP_MODE_LCLK specifically for RTL8821C on
> PCIe interfaces in rtw_update_lps_deep_mode(). Standard 802.11 LPS
> power saving and PCIe ASPM remain functional, preventing system lockups
> and firmware failures without affecting SDIO or USB variants.
> 
> Signed-off-by: Paolo Lazzaroni <eexto@xxxxxxx>
> ---
>  drivers/net/wireless/realtek/rtw88/main.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/net/wireless/realtek/rtw88/main.c b/drivers/net/wireless/realtek/rtw88/main.c
> index 0f23498b5..5bd854223 100644
> --- a/drivers/net/wireless/realtek/rtw88/main.c
> +++ b/drivers/net/wireless/realtek/rtw88/main.c
> @@ -1360,6 +1360,14 @@ static enum rtw_lps_deep_mode rtw_update_lps_deep_mode(struct rtw_dev *rtwdev,
>  	    !fw->feature)
>  		return LPS_DEEP_MODE_NONE;
>  
> +	/* RTL8821CE PCIe devices fail to wake up from 32kHz LCLK deep sleep
> +	 * in time for PCIe completion deadlines, leading to PCIe bus freeze

Completion timeout is already disabled for this chip.

> +	 * and communication timeouts.
> +	 */
> +	if (rtw_hci_type(rtwdev) == RTW_HCI_TYPE_PCIE &&
> +	    chip->id == RTW_CHIP_TYPE_8821C)
> +		return LPS_DEEP_MODE_NONE;
> +
>  	if ((chip->lps_deep_mode_supported & BIT(LPS_DEEP_MODE_PG)) &&
>  	    rtw_fw_feature_check(fw, FW_FEATURE_PG))
>  		return LPS_DEEP_MODE_PG;

However, I'm not saying it's necessarily wrong to disable deep PS for
this chip completely. I'm just objecting to your LLM's conclusions.