[PATCH rtw-next v6 0/4] wifi: rtw88: sdio: Fix unhandled RX request interrupt storm

[PATCH rtw-next v6 0/4] wifi: rtw88: sdio: Fix unhandled RX request interrupt storm

[Alastair D'Silva]

On 3081-based SDIO chips (observed on RTL8821CS; RTL8822CS is inferred to
be affected as it shares the 3081 architecture), hardware does not
automatically clear the REG_SDIO_HISR_RX_REQUEST status bit when the RX
FIFO becomes empty. Masking this bit out in software before writing back
to HISR prevented it from ever being acknowledged in hardware, trapping
the CPU core in an infinite interrupt storm that locked up the system upon
receiving network traffic.

This series fixes the interrupt storm on 3081 chips and addresses
related SDIO lifecycle, locking, and error handling issues:

- Patch 1 returns error codes from rtw_sdio_rxfifo_recv() on allocation
  or read failures so the caller stops immediately instead of burning
  through the loop budget.
- Patch 2 tracks operational state via rtwsdio->running protected by an
  irq_lock mutex (using a mutex as SDIO bus operations sleep), serializes
  start/stop state transitions under sdio_claim_host() and irq_lock, and
  cancels the TX worker synchronously on stop.
- Patch 3 fixes the interrupt storm by splitting
  rtw_sdio_handle_interrupt() into 8051 and 3081 paths. On 3081,
  interrupts are masked via HIMR, acknowledged via W1C writeback,
  serviced, and re-enabled under irq_lock if still running.
- Patch 4 refactors rtw_sdio_rx_isr() into separate 8051 and 3081 variants
  to clarify the differences in register width and HISR handling without
  any logic changes.

Hardware Validation:
Validated on an Allwinner H618 board (Mellow Fly-C5) with RTL8821CS SDIO
on the sunxi-mmc host controller (which dispatches SDIO interrupts via the
ksdioirqd thread rather than MMC_CAP2_SDIO_IRQ_NOTHREAD / sdio_irq_work)
running Linux 7.2.10, with policy routing configured and verified via
interface byte counters so all test traffic traversed wlan0 exclusively:
- RX test (10s iperf3 to board): 41.2 MB sent (34.6 Mbits/sec),
  40.4 MB received (33.8 Mbits/sec), with zero stalls, zero lockups, and
  no interrupt storm.
- TX test (10s iperf3 -R from board): 45.6 MB sent (38.2 Mbits/sec),
  44.4 MB received (37.2 Mbits/sec).
- Bidirectional test (10s iperf3 --bidir simultaneous TX and RX):
  RX 25.4 MB sent (21.3 Mbits/sec) / 24.2 MB received (20.2 Mbits/sec)
  concurrently with TX 10.2 MB sent (8.53 Mbits/sec) / 9.62 MB received
  (8.05 Mbits/sec).
- ksdioirqd/mmc1 CPU utilization remained at ~3.5% under load, and dmesg
  verified clean with zero warnings, traces, or hangs.

Differences in v6:
- Cover letter: Clarified that RTL8821CS was observed and tested while
  RTL8822CS is inferred from sharing the 3081 architecture, and noted that
  testing was performed on sunxi-mmc (ksdioirqd) per Luka Gejak. Added
  details below the cut line on how REG_SDIO_HISR_RX_REQUEST level
  sensitivity was verified on hardware.
- Patch 1: Added Reviewed-by from Luka Gejak.
- Patch 2: Dropped the rtw_sdio_deinit() helper and probe error path label
  rename per Luka Gejak, and refined the irq_lock comment in sdio.h.
- Patch 3: Replaced goto out with if (hisr) block to avoid mixing goto
  with cleanup.h helpers in rtw_sdio_handle_interrupt(), and documented
  why the full HISR word is written back on 3081 (matching all non-8723BS
  SDIO chips) and that REG_SDIO_HISR_RX_REQUEST is level-sensitive to RX
  FIFO occupancy (verified on hardware), addressing Luka Gejak's feedback.
- Patch 4: Added Reviewed-by from Luka Gejak.

Differences in v5:
- Patch 1: Added Acked-by from Ping-Ke Shih.
- Patch 2: Updated Fixes: tag to commit 28eaf7971a20 ("wifi: rtw88: sdio:
  add TX back-pressure and retry on page starvation") per discussion
  between Ping-Ke Shih and Luka Gejak.
- Patch 2: Replaced lockless running checks with an irq_lock mutex in
  struct rtw_sdio. Since SDIO I/O sleeps, a mutex is used instead of a
  spinlock. Enforced lock ordering (sdio_claim_host() -> irq_lock) in
  start and stop paths to avoid lock inversion with the MMC IRQ handler.
- Patch 2: Retained running checks in rtw_sdio_tx_handler() and
  rtw_sdio_handle_interrupt() to avoid races during stop.
- Patch 3: Protected the 3081 interrupt re-enable check under irq_lock
  (scoped_guard) per feedback from Ping-Ke Shih.
- Patch 4: Fixed comment formatting style in rtw_sdio_rx_isr_8051() per
  coding style rules.
- Patch 4: Added Acked-by from Ping-Ke Shih.

Differences in v4:
- Split pre-existing lifecycle and error handling issues into separate
  patches (Patches 1 and 2) prior to the storm fix (per Luka Gejak).
- Guard HIMR re-enabling with rtwsdio->running in the 3081 handler.
- Significantly reduced and streamlined commit messages across the series
  (per Ping-Ke Shih).
- Clarified in Patch 4 that it is a refactoring without logic changes,
  highlighting register width and HISR behavior (per Ping-Ke Shih).
- Tagged with rtw-next in subject prefix for NIPA testing.

---
Verifying REG_SDIO_HISR_RX_REQUEST level-sensitivity on RTL8821CS (3081):

To verify Luka's question on whether acknowledging REG_SDIO_HISR before
draining the RX FIFO can strand unread packets if rtw_sdio_rx_isr_3081()
exits early (upon hitting the 64 KB loop budget or an allocation/read
error), we instrumented rtw_sdio_handle_interrupt_3081() and
rtw_sdio_rx_isr_3081() on the RTL8821CS test board with a 4-point register
probe and a forced early-exit stress parameter (test_early_exit=1, which
forces rtw_sdio_rx_isr_3081() to break after reading a single RX DMA batch
so unread packets remain in the hardware FIFO):

1. Normal single-packet drain (FIFO emptied during ISR):
   - Entry: hisr=0x00800031 (BIT_RX_REQUEST=1), rx0_init=334
   - After W1C writeback (before FIFO read): post_ack_hisr=0x00800031,
     rx0_len=334. Even though software wrote 1 to clear BIT_RX_REQUEST,
     the hardware immediately kept BIT_RX_REQUEST asserted (1) because 334
     bytes of unread packet data were still sitting in the RX FIFO.
   - After rtw_sdio_rxfifo_recv() drained the 334 bytes: rx0_rem=0,
     post_drain_hisr=0x00800030 (BIT_RX_REQUEST=0). Only once the FIFO was
     empty AND the W1C acknowledge had occurred did BIT_RX_REQUEST drop to
     0.

2. Forced early exit with unread data remaining in the FIFO:
   - Under an iperf3 UDP flood with test_early_exit=1, the ISR exited
     after one read while unread packets remained in the FIFO (e.g.
     rx0_init=1538 -> post_ack_hisr=0x00800031 -> rx0_rem=3096).
   - Both post_drain_hisr and post_unmask_hisr read 0x00800031
     (BIT_RX_REQUEST=1), and the hardware immediately re-asserted the SDIO
     interrupt line upon unmasking HIMR. Over 1,920 forced early exits in
     a single burst, 100% re-asserted BIT_RX_REQUEST and re-triggered the
     interrupt without a single stalled packet.

Alastair D'Silva (4):
  wifi: rtw88: sdio: Handle allocation and read errors in
    rtw_sdio_rxfifo_recv
  wifi: rtw88: sdio: Track running state and cancel TX worker on stop
  wifi: rtw88: sdio: Fix unhandled RX request interrupt storm
  wifi: rtw88: sdio: Split rtw_sdio_rx_isr into 8051 and 3081 variants

 drivers/net/wireless/realtek/rtw88/sdio.c | 164 ++++++++++++++++------
 drivers/net/wireless/realtek/rtw88/sdio.h |   3 +
 2 files changed, 127 insertions(+), 40 deletions(-)

-- 
2.53.0

[PATCH rtw-next v6 1/4] wifi: rtw88: sdio: Handle allocation and read errors in rtw_sdio_rxfifo_recv

[Alastair D'Silva]

When dev_alloc_skb() or rtw_sdio_read_port() fails, rtw_sdio_rxfifo_recv()
returns without reading data. Because it returned void, the caller still
counted rx_len against the loop budget while leaving data stranded in the
FIFO.

Return an error code from rtw_sdio_rxfifo_recv() on failure and break out
of the receive loop in the caller immediately.

Fixes: 65371a3f14e7 ("wifi: rtw88: sdio: Add HCI implementation for SDIO based chipsets")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Reviewed-by: Luka Gejak <luka.gejak@linux.dev>
Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
---
 drivers/net/wireless/realtek/rtw88/sdio.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtw88/sdio.c b/drivers/net/wireless/realtek/rtw88/sdio.c
index dc2fd0f8f9ff..e39284b71837 100644
--- a/drivers/net/wireless/realtek/rtw88/sdio.c
+++ b/drivers/net/wireless/realtek/rtw88/sdio.c
@@ -1349,7 +1349,7 @@ static void rtw_sdio_rx_skb(struct rtw_dev *rtwdev, struct sk_buff *skb,
 	ieee80211_rx_irqsafe(rtwdev->hw, skb);
 }
 
-static void rtw_sdio_rxfifo_recv(struct rtw_dev *rtwdev, u32 rx_len)
+static int rtw_sdio_rxfifo_recv(struct rtw_dev *rtwdev, u32 rx_len)
 {
 	struct rtw_sdio *rtwsdio = (struct rtw_sdio *)rtwdev->priv;
 	const struct rtw_chip_info *chip = rtwdev->chip;
@@ -1366,12 +1366,12 @@ static void rtw_sdio_rxfifo_recv(struct rtw_dev *rtwdev, u32 rx_len)
 
 	skb = dev_alloc_skb(bufsz);
 	if (!skb)
-		return;
+		return -ENOMEM;
 
 	ret = rtw_sdio_read_port(rtwdev, skb->data, bufsz);
 	if (ret) {
 		dev_kfree_skb_any(skb);
-		return;
+		return ret;
 	}
 
 	while (true) {
@@ -1380,7 +1380,7 @@ static void rtw_sdio_rxfifo_recv(struct rtw_dev *rtwdev, u32 rx_len)
 					   &pkt_stat, &rx_status);
 		if (ret) {
 			dev_kfree_skb_any(skb);
-			return;
+			return ret;
 		}
 
 		pkt_offset = pkt_desc_sz + pkt_stat.drv_info_sz +
@@ -1416,11 +1416,14 @@ static void rtw_sdio_rxfifo_recv(struct rtw_dev *rtwdev, u32 rx_len)
 		skb_reserve(skb, curr_pkt_len);
 		rx_len -= curr_pkt_len;
 	}
+
+	return 0;
 }
 
 static void rtw_sdio_rx_isr(struct rtw_dev *rtwdev)
 {
 	u32 rx_len, hisr, total_rx_bytes = 0;
+	int ret;
 
 	do {
 		if (rtw_chip_wcpu_8051(rtwdev))
@@ -1431,7 +1434,9 @@ static void rtw_sdio_rx_isr(struct rtw_dev *rtwdev)
 		if (!rx_len)
 			break;
 
-		rtw_sdio_rxfifo_recv(rtwdev, rx_len);
+		ret = rtw_sdio_rxfifo_recv(rtwdev, rx_len);
+		if (ret)
+			break;
 
 		total_rx_bytes += rx_len;
 
-- 
2.53.0

[PATCH rtw-next v6 2/4] wifi: rtw88: sdio: Track running state and cancel TX worker on stop

[Alastair D'Silva]

When rtw_sdio_stop() disables interrupts, in-flight interrupt handlers or
delayed TX work may still run against a powered-down device.

Track the operational state in rtwsdio->running with an irq_lock mutex
(similar to PCI), check it at the entry of rtw_sdio_handle_interrupt()
and rtw_sdio_tx_handler(), serialize state transitions in rtw_sdio_start()
and rtw_sdio_stop() under sdio_claim_host() and irq_lock, and cancel the
TX worker synchronously in rtw_sdio_stop().

Fixes: 28eaf7971a20 ("wifi: rtw88: sdio: add TX back-pressure and retry on page starvation")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
---
 drivers/net/wireless/realtek/rtw88/sdio.c | 33 +++++++++++++++++++++--
 drivers/net/wireless/realtek/rtw88/sdio.h |  3 +++
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtw88/sdio.c b/drivers/net/wireless/realtek/rtw88/sdio.c
index e39284b71837..2e26e7a2a0fd 100644
--- a/drivers/net/wireless/realtek/rtw88/sdio.c
+++ b/drivers/net/wireless/realtek/rtw88/sdio.c
@@ -941,6 +941,8 @@ static void rtw_sdio_init(struct rtw_dev *rtwdev)
 {
 	struct rtw_sdio *rtwsdio = (struct rtw_sdio *)rtwdev->priv;
 
+	mutex_init(&rtwsdio->irq_lock);
+
 	if (rtw_is_8723bs(rtwdev))
 		rtwsdio->irq_mask = REG_SDIO_HIMR_RX_REQUEST;
 	else
@@ -1054,6 +1056,7 @@ static int rtw_sdio_8723bs_check_rqpn(struct rtw_dev *rtwdev)
 
 static int rtw_sdio_start(struct rtw_dev *rtwdev)
 {
+	struct rtw_sdio *rtwsdio = (struct rtw_sdio *)rtwdev->priv;
 	u32 clear;
 
 	if (rtw_is_8723bs(rtwdev)) {
@@ -1069,20 +1072,36 @@ static int rtw_sdio_start(struct rtw_dev *rtwdev)
 
 	rtw_sdio_enable_rx_aggregation(rtwdev);
 
+	sdio_claim_host(rtwsdio->sdio_func);
+
 	if (rtw_is_8723bs(rtwdev)) {
 		clear = rtw_read32(rtwdev, REG_SDIO_HISR) & RTW_SDIO_HISR_CLEAR_MASK;
 		if (clear)
 			rtw_write32(rtwdev, REG_SDIO_HISR, clear);
 	}
 
-	rtw_sdio_enable_interrupt(rtwdev);
+	scoped_guard(mutex, &rtwsdio->irq_lock) {
+		rtwsdio->running = true;
+		rtw_sdio_enable_interrupt(rtwdev);
+	}
+
+	sdio_release_host(rtwsdio->sdio_func);
 
 	return 0;
 }
 
 static void rtw_sdio_stop(struct rtw_dev *rtwdev)
 {
-	rtw_sdio_disable_interrupt(rtwdev);
+	struct rtw_sdio *rtwsdio = (struct rtw_sdio *)rtwdev->priv;
+
+	sdio_claim_host(rtwsdio->sdio_func);
+	scoped_guard(mutex, &rtwsdio->irq_lock) {
+		rtwsdio->running = false;
+		rtw_sdio_disable_interrupt(rtwdev);
+	}
+	sdio_release_host(rtwsdio->sdio_func);
+
+	cancel_delayed_work_sync(&rtwsdio->tx_handler_data->work);
 }
 
 static void rtw_sdio_deep_ps_enter(struct rtw_dev *rtwdev)
@@ -1470,6 +1489,11 @@ static void rtw_sdio_handle_interrupt(struct sdio_func *sdio_func)
 	rtwdev = hw->priv;
 	rtwsdio = (struct rtw_sdio *)rtwdev->priv;
 
+	scoped_guard(mutex, &rtwsdio->irq_lock) {
+		if (!rtwsdio->running)
+			return;
+	}
+
 	rtwsdio->irq_thread = current;
 
 	hisr = rtw_read32(rtwdev, REG_SDIO_HISR);
@@ -1703,6 +1727,11 @@ static void rtw_sdio_tx_handler(struct work_struct *work)
 	rtwdev = work_data->rtwdev;
 	rtwsdio = (struct rtw_sdio *)rtwdev->priv;
 
+	scoped_guard(mutex, &rtwsdio->irq_lock) {
+		if (!rtwsdio->running)
+			return;
+	}
+
 	if (!rtw_fw_feature_check(&rtwdev->fw, FW_FEATURE_TX_WAKE))
 		rtw_sdio_deep_ps_leave(rtwdev);
 
diff --git a/drivers/net/wireless/realtek/rtw88/sdio.h b/drivers/net/wireless/realtek/rtw88/sdio.h
index 6e7e6009744b..64266b54f595 100644
--- a/drivers/net/wireless/realtek/rtw88/sdio.h
+++ b/drivers/net/wireless/realtek/rtw88/sdio.h
@@ -168,6 +168,9 @@ struct rtw_sdio {
 	bool sdio3_bus_mode;
 
 	void *irq_thread;
+	bool running;
+	/* protect running state and enabling interrupts */
+	struct mutex irq_lock;
 
 	struct workqueue_struct *txwq;
 	struct rtw_sdio_work_data *tx_handler_data;
-- 
2.53.0

Re: [PATCH rtw-next v6 2/4] wifi: rtw88: sdio: Track running state and cancel TX worker on stop

[Luka Gejak]

Hi Alastair,

October 14, 2026 at 9:44 AM, "Alastair D'Silva" <alastair@d-silva.org> wrote:

>  static void rtw_sdio_stop(struct rtw_dev *rtwdev)
>  {                                                                                            > -     rtw_sdio_disable_interrupt(rtwdev);
> +     struct rtw_sdio *rtwsdio = (struct rtw_sdio *)rtwdev->priv;                             > +
> +     sdio_claim_host(rtwsdio->sdio_func);
> +     scoped_guard(mutex, &rtwsdio->irq_lock) {
> +             rtwsdio->running = false;
> +             rtw_sdio_disable_interrupt(rtwdev);
> +     }
> +     sdio_release_host(rtwsdio->sdio_func);
> +
> +     cancel_delayed_work_sync(&rtwsdio->tx_handler_data->work);
>  }

One thing about that cancel. The delayed work is the back pressure retry:
rtw_sdio_8723bs_reschedule_tx() re-arms it with queue_delayed_work() when
a page shortage parks a frame, and rtw_sdio_tx_kick_off() re-arms it with
mod_delayed_work() for every new frame. On 8723bs the frames that fill the
software FIFO past the watermark also stop the matching mac80211 queue
(ieee80211_stop_queue() in rtw_sdio_8723bs_stop_tx_queue()), and
rtw_sdio_start() undoes neither that nor tx_queue_stopped[]. The flag is
cleared in rtw_sdio_init_tx() and in rtw_sdio_8723bs_wake_tx_queue(), and
the second of those only runs after a write has gone out.

So a stop that lands while an access category is held back leaves the
queue stopped and its frames parked in rtwsdio->tx_queue[] with no work
queued to come back for them. It recovers as soon as anything transmits
on any queue, because that kicks the worker again and the handler walks
all queues, so I could not make it a permanent wedge. It does mean an
idle link can sit on those frames for a long time. Would it be worth
re-arming the worker at the end of rtw_sdio_start(), or clearing
tx_queue_stopped[] and waking the queues there?

Best regards,
Luka Gejak

[PATCH rtw-next v6 3/4] wifi: rtw88: sdio: Fix unhandled RX request interrupt storm

[Alastair D'Silva]

On 3081-based SDIO chips (e.g. RTL8821CS), hardware does not automatically
clear REG_SDIO_HISR_RX_REQUEST when the RX buffer is empty. Masking this
bit out before writing back to HISR prevents it from being acknowledged,
causing an infinite interrupt storm loop that locks up the system.

8051-based chips instead rely on hardware to clear this bit automatically
once the buffer is empty, and software must not clear it.

Split rtw_sdio_handle_interrupt() into separate 8051 and 3081 handlers.
For 3081, disable interrupts via HIMR, acknowledge all pending status
bits via W1C writeback (preserving the existing full status word
writeback used on non-RTL8723BS chips, now including
REG_SDIO_HISR_RX_REQUEST), service pending events, and re-enable
interrupts under irq_lock if still running.

On 3081 hardware, REG_SDIO_HISR_RX_REQUEST is level-sensitive to FIFO
occupancy: if unread packets remain in the FIFO when interrupts are
re-enabled (or if new packets arrived), the chip re-asserts
REG_SDIO_HISR_RX_REQUEST and re-triggers the IRQ line. For 8051 chips,
preserve the existing behavior.

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>
---
 drivers/net/wireless/realtek/rtw88/sdio.c | 74 ++++++++++++++++++-----
 1 file changed, 58 insertions(+), 16 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtw88/sdio.c b/drivers/net/wireless/realtek/rtw88/sdio.c
index 2e26e7a2a0fd..e459541b7678 100644
--- a/drivers/net/wireless/realtek/rtw88/sdio.c
+++ b/drivers/net/wireless/realtek/rtw88/sdio.c
@@ -1479,6 +1479,59 @@ static void rtw_sdio_rx_isr(struct rtw_dev *rtwdev)
 	} while (total_rx_bytes < SZ_64K && hisr & REG_SDIO_HISR_RX_REQUEST);
 }
 
+static void rtw_sdio_handle_interrupt_8051(struct rtw_dev *rtwdev, u32 hisr)
+{
+	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;
+		rtw_sdio_rx_isr(rtwdev);
+	}
+
+	/*
+	 * RTL8723BS keeps raising the interrupt after resume if undefined
+	 * status bits are written back, so acknowledge only the bits this
+	 * driver defines. Other chips keep the existing behaviour.
+	 */
+	if (rtw_is_8723bs(rtwdev))
+		hisr &= RTW_SDIO_HISR_CLEAR_MASK;
+
+	rtw_write32(rtwdev, REG_SDIO_HISR, hisr);
+}
+
+static void rtw_sdio_handle_interrupt_3081(struct rtw_dev *rtwdev, u32 hisr)
+{
+	struct rtw_sdio *rtwsdio = (struct rtw_sdio *)rtwdev->priv;
+
+	rtw_sdio_disable_interrupt(rtwdev);
+
+	/*
+	 * Acknowledge all pending status bits via W1C writeback. Unlike 8051,
+	 * 3081 requires REG_SDIO_HISR_RX_REQUEST to be explicitly cleared by
+	 * software.
+	 */
+	rtw_write32(rtwdev, REG_SDIO_HISR, hisr);
+
+	if (hisr & REG_SDIO_HISR_TXERR)
+		rtw_sdio_tx_err_isr(rtwdev);
+	if (hisr & REG_SDIO_HISR_RX_REQUEST)
+		rtw_sdio_rx_isr(rtwdev);
+
+	/*
+	 * Unmasking HIMR re-asserts the IRQ line if new packets arrived or if
+	 * unread data remains in the RX FIFO (e.g. if the 64KB budget was
+	 * reached or an RX error occurred). On 3081 hardware,
+	 * REG_SDIO_HISR_RX_REQUEST is level-sensitive to FIFO occupancy:
+	 * although cleared by the W1C writeback above, the chip automatically
+	 * re-asserts REG_SDIO_HISR_RX_REQUEST as long as the RX buffer is
+	 * non-empty, re-triggering the interrupt when unmasked.
+	 */
+	scoped_guard(mutex, &rtwsdio->irq_lock) {
+		if (rtwsdio->running)
+			rtw_sdio_enable_interrupt(rtwdev);
+	}
+}
+
 static void rtw_sdio_handle_interrupt(struct sdio_func *sdio_func)
 {
 	struct ieee80211_hw *hw = sdio_get_drvdata(sdio_func);
@@ -1497,24 +1550,13 @@ static void rtw_sdio_handle_interrupt(struct sdio_func *sdio_func)
 	rtwsdio->irq_thread = current;
 
 	hisr = rtw_read32(rtwdev, REG_SDIO_HISR);
-
-	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;
-		rtw_sdio_rx_isr(rtwdev);
+	if (hisr) {
+		if (rtw_chip_wcpu_8051(rtwdev))
+			rtw_sdio_handle_interrupt_8051(rtwdev, hisr);
+		else
+			rtw_sdio_handle_interrupt_3081(rtwdev, hisr);
 	}
 
-	/*
-	 * RTL8723BS keeps raising the interrupt after resume if undefined
-	 * status bits are written back, so acknowledge only the bits this
-	 * driver defines. Other chips keep the existing behaviour.
-	 */
-	if (rtw_is_8723bs(rtwdev))
-		hisr &= RTW_SDIO_HISR_CLEAR_MASK;
-
-	rtw_write32(rtwdev, REG_SDIO_HISR, hisr);
-
 	rtwsdio->irq_thread = NULL;
 }
 
-- 
2.53.0

Re: [PATCH rtw-next v6 3/4] wifi: rtw88: sdio: Fix unhandled RX request interrupt storm

[Luka Gejak]

Hi Alastair,

October 14, 2026 at 9:44 AM, "Alastair D'Silva" <alastair@d-silva.org> wrote:

> On 3081-based SDIO chips (e.g. RTL8821CS), hardware does not automatically
> clear REG_SDIO_HISR_RX_REQUEST when the RX buffer is empty. Masking this
> bit out before writing back to HISR prevents it from being acknowledged,
> causing an infinite interrupt storm loop that locks up the system.

In my opinion, I would reword this first sentance. Your own probe shows the
bit does clear, post_drain_hisr comes back as 0x00800030 once the FIFO is
empty, so what the hardware needs is the software acknowledge plus an
empty FIFO. The old code masked the acknowledge out of the writeback so
it never happened, which is the failure the second sentence describes.
As written the first one reads as if the bit could never be cleared and
the drain did not matter. The fix depends on the opposite reading.

Best regards,
Luka Gejak

[PATCH rtw-next v6 4/4] wifi: rtw88: sdio: Split rtw_sdio_rx_isr into 8051 and 3081 variants

[Alastair D'Silva]

Split rtw_sdio_rx_isr() into separate 8051 and 3081 variants to be
clear. The two differences between the architectures are:
- Register size: REG_SDIO_RX0_REQ_LEN is 16-bit on 8051, 32-bit on 3081.
- HISR behavior: 8051 re-reads REG_SDIO_HISR on each iteration, while
  3081 drains based on rx_len without re-reading HISR.

This is a refactoring without any logic changes.

Assisted-by: LLM
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Reviewed-by: Luka Gejak <luka.gejak@linux.dev>
Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
---
 drivers/net/wireless/realtek/rtw88/sdio.c | 58 +++++++++++++----------
 1 file changed, 33 insertions(+), 25 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtw88/sdio.c b/drivers/net/wireless/realtek/rtw88/sdio.c
index e459541b7678..3569aae0f2f0 100644
--- a/drivers/net/wireless/realtek/rtw88/sdio.c
+++ b/drivers/net/wireless/realtek/rtw88/sdio.c
@@ -1439,17 +1439,13 @@ static int rtw_sdio_rxfifo_recv(struct rtw_dev *rtwdev, u32 rx_len)
 	return 0;
 }
 
-static void rtw_sdio_rx_isr(struct rtw_dev *rtwdev)
+static void rtw_sdio_rx_isr_8051(struct rtw_dev *rtwdev)
 {
 	u32 rx_len, hisr, total_rx_bytes = 0;
 	int ret;
 
 	do {
-		if (rtw_chip_wcpu_8051(rtwdev))
-			rx_len = rtw_read16(rtwdev, REG_SDIO_RX0_REQ_LEN);
-		else
-			rx_len = rtw_read32(rtwdev, REG_SDIO_RX0_REQ_LEN);
-
+		rx_len = rtw_read16(rtwdev, REG_SDIO_RX0_REQ_LEN);
 		if (!rx_len)
 			break;
 
@@ -1459,33 +1455,45 @@ static void rtw_sdio_rx_isr(struct rtw_dev *rtwdev)
 
 		total_rx_bytes += rx_len;
 
-		if (rtw_chip_wcpu_8051(rtwdev)) {
-			/* Stop if no more RX requests are pending, even if
-			 * rx_len could be greater than zero in the next
-			 * iteration. This is needed because the RX buffer may
-			 * already contain data while either HW or FW are not
-			 * done filling that buffer yet. Still reading the
-			 * buffer can result in packets where
-			 * rtw_rx_pkt_stat.pkt_len is zero or points beyond the
-			 * end of the buffer.
-			 */
-			hisr = rtw_read32(rtwdev, REG_SDIO_HISR);
-		} else {
-			/* RTW_WCPU_3081 chips have improved hardware or
-			 * firmware and can use rx_len unconditionally.
-			 */
-			hisr = REG_SDIO_HISR_RX_REQUEST;
-		}
+		/*
+		 * Stop if no more RX requests are pending, even if
+		 * rx_len could be greater than zero in the next
+		 * iteration. This is needed because the RX buffer may
+		 * already contain data while either HW or FW are not
+		 * done filling that buffer yet. Still reading the
+		 * buffer can result in packets where
+		 * rtw_rx_pkt_stat.pkt_len is zero or points beyond the
+		 * end of the buffer.
+		 */
+		hisr = rtw_read32(rtwdev, REG_SDIO_HISR);
 	} while (total_rx_bytes < SZ_64K && hisr & REG_SDIO_HISR_RX_REQUEST);
 }
 
+static void rtw_sdio_rx_isr_3081(struct rtw_dev *rtwdev)
+{
+	u32 rx_len, total_rx_bytes = 0;
+	int ret;
+
+	do {
+		rx_len = rtw_read32(rtwdev, REG_SDIO_RX0_REQ_LEN);
+		if (!rx_len)
+			break;
+
+		ret = rtw_sdio_rxfifo_recv(rtwdev, rx_len);
+		if (ret)
+			break;
+
+		total_rx_bytes += rx_len;
+	} while (total_rx_bytes < SZ_64K);
+}
+
 static void rtw_sdio_handle_interrupt_8051(struct rtw_dev *rtwdev, u32 hisr)
 {
 	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;
-		rtw_sdio_rx_isr(rtwdev);
+		rtw_sdio_rx_isr_8051(rtwdev);
 	}
 
 	/*
@@ -1515,7 +1523,7 @@ static void rtw_sdio_handle_interrupt_3081(struct rtw_dev *rtwdev, u32 hisr)
 	if (hisr & REG_SDIO_HISR_TXERR)
 		rtw_sdio_tx_err_isr(rtwdev);
 	if (hisr & REG_SDIO_HISR_RX_REQUEST)
-		rtw_sdio_rx_isr(rtwdev);
+		rtw_sdio_rx_isr_3081(rtwdev);
 
 	/*
 	 * Unmasking HIMR re-asserts the IRQ line if new packets arrived or if
-- 
2.53.0

Re: [PATCH rtw-next v6 0/4] wifi: rtw88: sdio: Fix unhandled RX request interrupt storm

[Luka Gejak]

Hi Alastair,

October 14, 2026 at 9:44 AM, "Alastair D'Silva" <alastair@d-silva.org> wrote:

> On 3081-based SDIO chips (observed on RTL8821CS; RTL8822CS is inferred to
> be affected as it shares the 3081 architecture), hardware does not
> automatically clear the REG_SDIO_HISR_RX_REQUEST status bit when the RX
> FIFO becomes empty. Masking this bit out in software before writing back
> to HISR prevented it from ever being acknowledged in hardware, trapping
> the CPU core in an infinite interrupt storm that locked up the system upon
> receiving network traffic.

There are three 3081 parts with an SDIO front end, not two. 8822BS is
RTW_WCPU_3081 as well (rtw8822b.c:2527) and rtw8822bs.c is built as
rtw88_8822bs.o, so naming 8821CS and 8822CS only leaves it out. Patch 3
changes the interrupt path for all three at once and only the 8821CS was
probed, which is the one thing I would add to a series that Cc's stable.
If there is no run on 8822BS and 8822CS to hand, saying the same for both
would do, the way the cover already does for 8822CS.

Best regards,
Luka Gejak