linux-kernel - [PATCH net v3] net: mdio: aspeed: add dummy read to avoid read-after-write issue

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251211-aspeed_mdio_add_dummy_read-v3-1-382868869004@aspeedtech.com>
Date: Thu, 11 Dec 2025 14:24:58 +0800
From: Jacky Chou <jacky_chou@...eedtech.com>
To: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Joel Stanley
	<joel@....id.au>, Andrew Jeffery <andrew@...econstruct.com.au>, Potin Lai
	<potin.lai@...ntatw.com>
CC: <netdev@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-aspeed@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>, "Andrew
 Jeffery" <andrew@...id.au>, Jacky Chou <jacky_chou@...eedtech.com>
Subject: [PATCH net v3] net: mdio: aspeed: add dummy read to avoid
 read-after-write issue

The Aspeed MDIO controller may return incorrect data when a read operation
follows immediately after a write. Due to a controller bug, the subsequent
read can latch stale data, causing the polling logic to terminate earlier
than expected.

To work around this hardware issue, insert a dummy read after each write
operation. This ensures that the next actual read returns the correct
data and prevents premature polling exit.

This workaround has been verified to stabilize MDIO transactions on
affected Aspeed platforms.

Fixes: f160e99462c6 ("net: phy: Add mdio-aspeed")
Signed-off-by: Jacky Chou <jacky_chou@...eedtech.com>
---
Changes in v3:
- Remove (void)
- Link to v2: https://lore.kernel.org/r/20251209-aspeed_mdio_add_dummy_read-v2-1-5f6061641989@aspeedtech.com

Changes in v2:
- Updated the Fixes: tag
- Link to v1: https://lore.kernel.org/r/20251208-aspeed_mdio_add_dummy_read-v1-1-0a1861ad2161@aspeedtech.com
---
 drivers/net/mdio/mdio-aspeed.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/net/mdio/mdio-aspeed.c b/drivers/net/mdio/mdio-aspeed.c
index e55be6dc9ae7..d6b9004c61dc 100644
--- a/drivers/net/mdio/mdio-aspeed.c
+++ b/drivers/net/mdio/mdio-aspeed.c
@@ -63,6 +63,13 @@ static int aspeed_mdio_op(struct mii_bus *bus, u8 st, u8 op, u8 phyad, u8 regad,
 
 	iowrite32(ctrl, ctx->base + ASPEED_MDIO_CTRL);
 
+	/* Workaround for read-after-write issue.
+	 * The controller may return stale data if a read follows immediately
+	 * after a write. A dummy read forces the hardware to update its
+	 * internal state, ensuring that the next real read returns correct data.
+	 */
+	ioread32(ctx->base + ASPEED_MDIO_CTRL);
+
 	return readl_poll_timeout(ctx->base + ASPEED_MDIO_CTRL, ctrl,
 				!(ctrl & ASPEED_MDIO_CTRL_FIRE),
 				ASPEED_MDIO_INTERVAL_US,

---
base-commit: 6bcb7727d9e612011b70d64a34401688b986d6ab
change-id: 20251208-aspeed_mdio_add_dummy_read-587ab8808817

Best regards,
-- 
Jacky Chou <jacky_chou@...eedtech.com>