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

[Paolo Lazzaroni <eexto@aol.com>]

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
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.

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@aol.com>
---
 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
+	 * 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;
-- 
2.43.0