[PATCH] wifi: rtw88: sdio: Fix unhandled RX request interrupt storm

[Alastair D'Silva <alastair@d-silva.org>]

In rtw_sdio_handle_interrupt(), the HISR status register is cleared using
Write-1-to-Clear (W1C) semantics. However, the driver masks out the
REG_SDIO_HISR_RX_REQUEST bit in the local 'hisr' variable before writing
it back, causing a 0 to be written to that bit.

This prevents the RX request interrupt from being acknowledged and
cleared by the hardware, trapping the CPU core in an infinite interrupt
storm loop upon receiving packets and triggering RCU stalls and system
lockups.

Remove the masking of REG_SDIO_HISR_RX_REQUEST so that the interrupt
status is correctly written back as a 1 and acknowledged.

Fixes: 65371a3f14e7 ("wifi: rtw88: sdio: Add HCI implementation for SDIO based chipsets")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
---

Notes:
    Tested on Mellow Fly-C5 (Allwinner H618) with onboard Realtek RTL8821CS
    SDIO Wi-Fi under Armbian, resolving immediate RCU stalls upon packet arrival
    and achieving stable Wi-Fi throughput.

 drivers/net/wireless/realtek/rtw88/sdio.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtw88/sdio.c b/drivers/net/wireless/realtek/rtw88/sdio.c
index 5b40d74b16ee..73686b462957 100644
--- a/drivers/net/wireless/realtek/rtw88/sdio.c
+++ b/drivers/net/wireless/realtek/rtw88/sdio.c
@@ -1090,10 +1090,8 @@ static void rtw_sdio_handle_interrupt(struct sdio_func *sdio_func)
 
 	if (hisr & REG_SDIO_HISR_TXERR)
 		rtw_sdio_tx_err_isr(rtwdev);
-	if (hisr & REG_SDIO_HISR_RX_REQUEST) {
-		hisr &= ~REG_SDIO_HISR_RX_REQUEST;
+	if (hisr & REG_SDIO_HISR_RX_REQUEST)
 		rtw_sdio_rx_isr(rtwdev);
-	}
 
 	rtw_write32(rtwdev, REG_SDIO_HISR, hisr);
 
-- 
2.53.0