linux-kernel - [PATCH net v2] net: spacemit: Clarify stat timeout comments and messages

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Message-Id: <20260121-k1-ethernet-clarify-stat-timeout-v2-1-76ff1a1168d9@iscas.ac.cn>
Date: Wed, 21 Jan 2026 10:17:18 +0800
From: Vivian Wang <wangruikang@...as.ac.cn>
To: Andrew Lunn <andrew+netdev@...n.ch>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Yixun Lan <dlan@...too.org>
Cc: Chukun Pan <amadeus@....edu.cn>, 
 Michael Opdenacker <michael.opdenacker@...tcommit.com>, 
 netdev@...r.kernel.org, linux-riscv@...ts.infradead.org, 
 spacemit@...ts.linux.dev, linux-kernel@...r.kernel.org, 
 Vivian Wang <wangruikang@...as.ac.cn>
Subject: [PATCH net v2] net: spacemit: Clarify stat timeout comments and
 messages

Someone did run into this timeout in the wild [1], and it turns out to
be related to the PHY reference clock stopping.

Improve the comments and error message prints around this to reflect the
better understanding of how this could happen.

This patch isn't a fix for the problem per se, since it is hardware
behavior. The new message and comments, however, should direct those
running into this on new hardware towards a fix.

Link: https://lore.kernel.org/r/20260119141620.1318102-1-amadeus@jmu.edu.cn/ # [1]
Fixes: bfec6d7f2001 ("net: spacemit: Add K1 Ethernet MAC")
Signed-off-by: Vivian Wang <wangruikang@...as.ac.cn>
---
Changes in v2:
- Add "Fixes" and retarget to net (Andrew)
- Link to v1: https://lore.kernel.org/r/20260120-k1-ethernet-clarify-stat-timeout-v1-1-108cf928d1b3@iscas.ac.cn
---
 drivers/net/ethernet/spacemit/k1_emac.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/spacemit/k1_emac.c b/drivers/net/ethernet/spacemit/k1_emac.c
index 220eb5ce7583..387f26ff7714 100644
--- a/drivers/net/ethernet/spacemit/k1_emac.c
+++ b/drivers/net/ethernet/spacemit/k1_emac.c
@@ -1099,7 +1099,14 @@ static int emac_read_stat_cnt(struct emac_priv *priv, u8 cnt, u32 *res,
 					100, 10000);

 	if (ret) {
-		netdev_err(priv->ndev, "Read stat timeout\n");
+		/*
+		 * If you run into this, one possibility is that even though the
+		 * interface is up the PHY may have stopped its clock anyway for
+		 * power saving. This MAC doesn't like that, so configure your
+		 * PHY to not do that.
+		 */
+		dev_err_ratelimited(&priv->ndev->dev,
+				    "Read stat timeout. PHY clock stopped?\n");
 		return ret;
 	}

@@ -1148,16 +1155,20 @@ static void emac_stats_update(struct emac_priv *priv)
 	assert_spin_locked(&priv->stats_lock);

 	if (!netif_running(priv->ndev) || !netif_device_present(priv->ndev)) {
-		/* Not up, don't try to update */
+		/*
+		 * Not up, don't try to update. If the PHY is stopped, reading
+		 * stats would time out.
+		 */
 		return;
 	}

 	for (i = 0; i < sizeof(priv->tx_stats) / sizeof(*tx_stats); i++) {
 		/*
-		 * If reading stats times out, everything is broken and there's
-		 * nothing we can do. Reading statistics also can't return an
-		 * error, so just return without updating and without
-		 * rescheduling.
+		 * If reading stats times out anyway, the stat registers will be
+		 * stuck, and we can't really recover from that.
+		 *
+		 * Reading statistics also can't return an error, so just return
+		 * without updating and without rescheduling.
 		 */
 		if (emac_tx_read_stat_cnt(priv, i, &res))
 			return;

---
base-commit: a9f470594c50ab1ddf25b21a00ca4d3166057f3b
change-id: 20260120-k1-ethernet-clarify-stat-timeout-d221fcd3aaa8

Best regards,
-- 
Vivian "dramforever" Wang