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

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Message-ID: <f53fcaf3-0154-4cc7-87be-ab815fa8b6f5@lunn.ch>
Date: Thu, 11 Dec 2025 14:29:20 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Jacky Chou <jacky_chou@...eedtech.com>
Cc: 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>, 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>
Subject: Re: [PATCH net v3] net: mdio: aspeed: add dummy read to avoid
 read-after-write issue

On Thu, Dec 11, 2025 at 02:24:58PM +0800, Jacky Chou wrote:
> 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>

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew