[PATCH] wifi: ath11k: fix ring-buffer corruption

[Johan Hovold]

Users of the Lenovo ThinkPad X13s have reported that Wi-Fi sometimes
breaks and the log fills up with errors like:

	ath11k_pci 0006:01:00.0: HTC Rx: insufficient length, got 1484, expected 1492
	ath11k_pci 0006:01:00.0: HTC Rx: insufficient length, got 1460, expected 1484

which based on a quick look at the driver seemed to indicate some kind
of ring-buffer corruption.

Miaoqing Pan tracked it down to the host seeing the updated destination
ring head pointer before the updated descriptor, and the error handling
for that in turn leaves the ring buffer in an inconsistent state.

Add the missing the read barrier to make sure that the descriptor is
read after the head pointer to address the root cause of the corruption.

The error handling can be fixed separately in case there can ever be
actual zero-length descriptors.

FIXME: remove WARN_ON_ONCE() added for verification purposes

Tested-on: WCN6855 hw2.1 WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.41

Fixes: d5c65159f289 ("ath11k: driver for Qualcomm IEEE 802.11ax devices")
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218623
Link: https://lore.kernel.org/20250310010217.3845141-3-quic_miaoqing@xxxxxxxxxxx
Cc: Miaoqing Pan <quic_miaoqing@xxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx	# 5.6
Signed-off-by: Johan Hovold <johan+linaro@xxxxxxxxxx>
---
 drivers/net/wireless/ath/ath11k/ce.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/wireless/ath/ath11k/ce.c b/drivers/net/wireless/ath/ath11k/ce.c
index e66e86bdec20..423b970e288c 100644
--- a/drivers/net/wireless/ath/ath11k/ce.c
+++ b/drivers/net/wireless/ath/ath11k/ce.c
@@ -393,8 +393,12 @@ static int ath11k_ce_completed_recv_next(struct ath11k_ce_pipe *pipe,
 		goto err;
 	}
 
+	/* Make sure descriptor is read after the head pointer. */
+	dma_rmb();
+
 	*nbytes = ath11k_hal_ce_dst_status_get_length(desc);
 	if (*nbytes == 0) {
+		WARN_ON_ONCE(1);	// FIXME: remove
 		ret = -EIO;
 		goto err;
 	}
-- 
2.48.1