[PATCH v3 1/4] wifi: ath12k: fix dest ring-buffer corruption

[Johan Hovold <johan+linaro@kernel.org>]

Add the missing memory barrier to make sure that destination ring
descriptors are read after the head pointers to avoid using stale data
on weakly ordered architectures like aarch64.

The barrier is added to the ath12k_hal_srng_access_begin() helper for
symmetry with follow-on fixes for source ring buffer corruption which
will add barriers to ath12k_hal_srng_access_end().

Tested-on: WCN7850 hw2.0 WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3

Fixes: d889913205cf ("wifi: ath12k: driver for Qualcomm Wi-Fi 7 devices")
Cc: stable@vger.kernel.org	# 6.3
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
---
 drivers/net/wireless/ath/ath12k/ce.c  |  3 ---
 drivers/net/wireless/ath/ath12k/hal.c | 17 ++++++++++++++---
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/net/wireless/ath/ath12k/ce.c b/drivers/net/wireless/ath/ath12k/ce.c
index 3f3439262cf4..f7c15b547504 100644
--- a/drivers/net/wireless/ath/ath12k/ce.c
+++ b/drivers/net/wireless/ath/ath12k/ce.c
@@ -433,9 +433,6 @@ static int ath12k_ce_completed_recv_next(struct ath12k_ce_pipe *pipe,
 		goto err;
 	}
 
-	/* Make sure descriptor is read after the head pointer. */
-	dma_rmb();
-
 	*nbytes = ath12k_hal_ce_dst_status_get_length(desc);
 
 	*skb = pipe->dest_ring->skb[sw_index];
diff --git a/drivers/net/wireless/ath/ath12k/hal.c b/drivers/net/wireless/ath/ath12k/hal.c
index a301898e5849..f8bd3837b9dc 100644
--- a/drivers/net/wireless/ath/ath12k/hal.c
+++ b/drivers/net/wireless/ath/ath12k/hal.c
@@ -2143,13 +2143,24 @@ void *ath12k_hal_srng_src_get_next_reaped(struct ath12k_base *ab,
 
 void ath12k_hal_srng_access_begin(struct ath12k_base *ab, struct hal_srng *srng)
 {
+	u32 hp;
+
 	lockdep_assert_held(&srng->lock);
 
-	if (srng->ring_dir == HAL_SRNG_DIR_SRC)
+	if (srng->ring_dir == HAL_SRNG_DIR_SRC) {
 		srng->u.src_ring.cached_tp =
 			*(volatile u32 *)srng->u.src_ring.tp_addr;
-	else
-		srng->u.dst_ring.cached_hp = READ_ONCE(*srng->u.dst_ring.hp_addr);
+	} else {
+		hp = READ_ONCE(*srng->u.dst_ring.hp_addr);
+
+		if (hp != srng->u.dst_ring.cached_hp) {
+			srng->u.dst_ring.cached_hp = hp;
+			/* Make sure descriptor is read after the head
+			 * pointer.
+			 */
+			dma_rmb();
+		}
+	}
 }
 
 /* Update cached ring head/tail pointers to HW. ath12k_hal_srng_access_begin()
-- 
2.49.0