[PATCH net v2] net: renesas: rswitch: Fix timestamp feature after all descriptors are used

[Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>]

The timestamp descriptors were intended to act cyclically. Descriptors
from index 0 through gq->ring_size - 1 contain actual information, and
the last index (gq->ring_size) should have LINKFIX to indicate
the first index 0 descriptor. However, thie LINKFIX value is missing,
causing the timestamp feature to stop after all descriptors are used.
To resolve this issue, set the LINKFIX to the timestamp descritors.

Reported-by: Phong Hoang <phong.hoang.wz@renesas.com>
Fixes: 33f5d733b589 ("net: renesas: rswitch: Improve TX timestamp accuracy")
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
---
 Since I got this report locally, I didn't add Closes: tag.

 Changes from v1:
https://lore.kernel.org/all/20230607064402.1795548-1-yoshihiro.shimoda.uh@renesas.com/
 - Fix typo in the subject.

 drivers/net/ethernet/renesas/rswitch.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/renesas/rswitch.c b/drivers/net/ethernet/renesas/rswitch.c
index aace87139cea..049adbf5a642 100644
--- a/drivers/net/ethernet/renesas/rswitch.c
+++ b/drivers/net/ethernet/renesas/rswitch.c
@@ -420,7 +420,7 @@ static int rswitch_gwca_queue_format(struct net_device *ndev,
 }
 
 static void rswitch_gwca_ts_queue_fill(struct rswitch_private *priv,
-				       int start_index, int num)
+				       int start_index, int num, bool last)
 {
 	struct rswitch_gwca_queue *gq = &priv->gwca.ts_queue;
 	struct rswitch_ts_desc *desc;
@@ -431,6 +431,12 @@ static void rswitch_gwca_ts_queue_fill(struct rswitch_private *priv,
 		desc = &gq->ts_ring[index];
 		desc->desc.die_dt = DT_FEMPTY_ND | DIE;
 	}
+
+	if (last) {
+		desc = &gq->ts_ring[gq->ring_size];
+		rswitch_desc_set_dptr(&desc->desc, gq->ring_dma);
+		desc->desc.die_dt = DT_LINKFIX;
+	}
 }
 
 static int rswitch_gwca_queue_ext_ts_fill(struct net_device *ndev,
@@ -941,7 +947,7 @@ static void rswitch_ts(struct rswitch_private *priv)
 	}
 
 	num = rswitch_get_num_cur_queues(gq);
-	rswitch_gwca_ts_queue_fill(priv, gq->dirty, num);
+	rswitch_gwca_ts_queue_fill(priv, gq->dirty, num, false);
 	gq->dirty = rswitch_next_queue_index(gq, false, num);
 }
 
@@ -1780,7 +1786,7 @@ static int rswitch_init(struct rswitch_private *priv)
 	if (err < 0)
 		goto err_ts_queue_alloc;
 
-	rswitch_gwca_ts_queue_fill(priv, 0, TS_RING_SIZE);
+	rswitch_gwca_ts_queue_fill(priv, 0, TS_RING_SIZE, true);
 	INIT_LIST_HEAD(&priv->gwca.ts_info_list);
 
 	for (i = 0; i < RSWITCH_NUM_PORTS; i++) {
-- 
2.25.1