wifi: ath11k: fix dest ring-buffer corruption

commit 8c1ba50 upstream.

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 ath11k_hal_srng_access_begin() helper for
symmetry with follow-on fixes for source ring buffer corruption which
will add barriers to ath11k_hal_srng_access_end().

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

Fixes: d5c6515 ("ath11k: driver for Qualcomm IEEE 802.11ax devices")
Cc: stable@vger.kernel.org	# 5.6
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: Baochen Qiang <quic_bqiang@quicinc.com>
Link: https://patch.msgid.link/20250604143457.26032-2-johan+linaro@kernel.org
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: jhovold

drivers/net/wireless/ath/ath11k/ce.c

@@ -393,9 +393,6 @@ 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);
 
 	*skb = pipe->dest_ring->skb[sw_index];

drivers/net/wireless/ath/ath11k/dp_rx.c

@@ -2650,9 +2650,6 @@ int ath11k_dp_process_rx(struct ath11k_base *ab, int ring_id,
 try_again:
 	ath11k_hal_srng_access_begin(ab, srng);
 
-	/* Make sure descriptor is read after the head pointer. */
-	dma_rmb();
-
 	while (likely(desc =
 	      (struct hal_reo_dest_ring *)ath11k_hal_srng_dst_get_next_entry(ab,
 									     srng))) {

drivers/net/wireless/ath/ath11k/hal.c

@@ -823,13 +823,23 @@ u32 *ath11k_hal_srng_src_peek(struct ath11k_base *ab, struct hal_srng *srng)
 
 void ath11k_hal_srng_access_begin(struct ath11k_base *ab, struct hal_srng *srng)
 {
+	u32 hp;
+
 	lockdep_assert_held(&srng->lock);
 
 	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);
+		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();
+		}
 
 		/* Try to prefetch the next descriptor in the ring */
 		if (srng->flags & HAL_SRNG_FLAGS_CACHED)